The team detected signals from the Magellanic Stream using the 4.5m radio telescope at Leuschner Observatory. Images of the observed region in galactic coordinates showed high-velocity gases from -100 to -350 km/s, consistent with the Magellanic Stream. A velocity map matched previous studies, and higher intensities near the galactic pole aligned with expectations. Issues with intensity calibration and single polarization data collection impacted accuracy but detection of the stream was achieved.
A kiloparsec scale_internal_shock_collision_in_the_jet_of_a_nearby_radio_galaxySérgio Sacani
This document summarizes observations of a collision between two knots (B and C) in the jet of the nearby radio galaxy 3C 264 using Hubble Space Telescope imaging from 1994 to 2014. Knot B was found to have an apparent speed of 7.0c, much faster than other knots. Knots B and C showed simultaneous brightening in 2014, indicating the beginning of their collision. Analysis suggests the collision will dissipate kinetic energy with a conversion efficiency to radiation of at least 0.1%, providing a way to study particle acceleration in astrophysical jets.
A gravitational-wave standard siren measurement of the Hubble constantSérgio Sacani
On 17 August 2017, the Advanced LIGO1
and Virgo2
detectors
observed the gravitational-wave event GW170817—a strong signal
from the merger of a binary neutron-star system3
. Less than two
seconds after the merger, a γ-ray burst (GRB 170817A) was detected
within a region of the sky consistent with the LIGO–Virgo-derived
location of the gravitational-wave source4–6. This sky region was
subsequently observed by optical astronomy facilities7
, resulting
in the identification8–13 of an optical transient signal within
about ten arcseconds of the galaxy NGC 4993. This detection of
GW170817 in both gravitational waves and electromagnetic waves
represents the first ‘multi-messenger’ astronomical observation.
Such observations enable GW170817 to be used as a ‘standard
siren’14–18 (meaning that the absolute distance to the source can be
determined directly from the gravitational-wave measurements)
to measure the Hubble constant. This quantity represents the local
expansion rate of the Universe, sets the overall scale of the Universe
and is of fundamental importance to cosmology. Here we report a
measurement of the Hubble constant that combines the distance
to the source inferred purely from the gravitational-wave signal
with the recession velocity inferred from measurements of the
redshift using the electromagnetic data. In contrast to previous
measurements, ours does not require the use of a cosmic ‘distance
ladder’19: the gravitational-wave analysis can be used to estimate
the luminosity distance out to cosmological scales directly, without
the use of intermediate astronomical distance measurements. We
determine the Hubble constant to be about 70 kilometres per
second per megaparsec. This value is consistent with existing
measurements20,21, while being completely independent of them.
Additional standard siren measurements from future gravitationalwave
sources will enable the Hubble constant to be constrained to
high precision.
Mapping spiral structure on the far side of the Milky WaySérgio Sacani
Little is known about the portion of the Milky Way lying beyond the Galactic center at distances
of more than 9 kiloparsec from the Sun. These regions are opaque at optical wavelengths
because of absorption by interstellar dust, and distances are very large and hard to measure.
We report a direct trigonometric parallax distance of 20:4þ2:8
2:2 kiloparsec obtained with the Very
Long Baseline Array to a water maser source in a region of active star formation. These
measurements allow us to shed light on Galactic spiral structure by locating the ScutumCentaurus
spiral arm as it passes through the far side of the Milky Way and to validate a
kinematic method for determining distances in this region on the basis of transverse motions.
This document discusses three approaches to adding antennas to the GMRT array to obtain denser uv coverage and a better signal-to-noise ratio. Approach 1 involves adding a single antenna and solving an equation to determine its coordinates but was found to not have a unique solution. Approach 2 adds antennas in a rectangular patch and simulates the coverage, selecting a set of three antennas. Approach 3 visually analyzes coverage from adding antennas individually at grid points in the patch, selecting a combination of three grids. The combination from Approach 3 agreed with locations from Approach 2.
Towards the identification of the primary particle nature by the radiodetecti...Ahmed Ammar Rebai PhD
This document summarizes a study using the CODALEMA experiment to analyze radio signals from air showers and identify properties of primary cosmic ray particles. It describes:
1) Analyzing time delays of radio signals compared to a plane wavefront hypothesis and finding systematic deviations, indicating the wavefront is curved.
2) Developing a model to reconstruct the emission center position based on fitting time delays to a parabolic function dependent on curvature radius and antenna distances.
3) Applying the model to 450 selected CODALEMA events and comparing reconstructed shower core positions to results from other models, finding consistency.
1) Lunar Orbiter tracking data revealed large mass concentrations (mascons) beneath the lunar maria.
2) The largest mascons were found beneath Mare Imbrium, Mare Serenitatis, Mare Crisium, Mare Humorum, and Mare Nectaris.
3) The mascons suggest a relationship between the formation of the maria and large impact events on the lunar surface.
Water vapour absorption in the clear atmosphere of a Neptune-sized exoplanetGOASA
1) The transmission spectrum of the exoplanet HAT-P-11b was observed using Hubble and Spitzer space telescopes.
2) Water vapor absorption was detected at 1.4 micrometers in the atmosphere, indicating a clear atmosphere down to 1 mbar pressure.
3) The detection of water vapor and relatively large atmospheric scale height places an upper limit on the abundance of heavy elements in the atmosphere of around 700 times the solar value, consistent with core accretion planet formation theories.
A kiloparsec scale_internal_shock_collision_in_the_jet_of_a_nearby_radio_galaxySérgio Sacani
This document summarizes observations of a collision between two knots (B and C) in the jet of the nearby radio galaxy 3C 264 using Hubble Space Telescope imaging from 1994 to 2014. Knot B was found to have an apparent speed of 7.0c, much faster than other knots. Knots B and C showed simultaneous brightening in 2014, indicating the beginning of their collision. Analysis suggests the collision will dissipate kinetic energy with a conversion efficiency to radiation of at least 0.1%, providing a way to study particle acceleration in astrophysical jets.
A gravitational-wave standard siren measurement of the Hubble constantSérgio Sacani
On 17 August 2017, the Advanced LIGO1
and Virgo2
detectors
observed the gravitational-wave event GW170817—a strong signal
from the merger of a binary neutron-star system3
. Less than two
seconds after the merger, a γ-ray burst (GRB 170817A) was detected
within a region of the sky consistent with the LIGO–Virgo-derived
location of the gravitational-wave source4–6. This sky region was
subsequently observed by optical astronomy facilities7
, resulting
in the identification8–13 of an optical transient signal within
about ten arcseconds of the galaxy NGC 4993. This detection of
GW170817 in both gravitational waves and electromagnetic waves
represents the first ‘multi-messenger’ astronomical observation.
Such observations enable GW170817 to be used as a ‘standard
siren’14–18 (meaning that the absolute distance to the source can be
determined directly from the gravitational-wave measurements)
to measure the Hubble constant. This quantity represents the local
expansion rate of the Universe, sets the overall scale of the Universe
and is of fundamental importance to cosmology. Here we report a
measurement of the Hubble constant that combines the distance
to the source inferred purely from the gravitational-wave signal
with the recession velocity inferred from measurements of the
redshift using the electromagnetic data. In contrast to previous
measurements, ours does not require the use of a cosmic ‘distance
ladder’19: the gravitational-wave analysis can be used to estimate
the luminosity distance out to cosmological scales directly, without
the use of intermediate astronomical distance measurements. We
determine the Hubble constant to be about 70 kilometres per
second per megaparsec. This value is consistent with existing
measurements20,21, while being completely independent of them.
Additional standard siren measurements from future gravitationalwave
sources will enable the Hubble constant to be constrained to
high precision.
Mapping spiral structure on the far side of the Milky WaySérgio Sacani
Little is known about the portion of the Milky Way lying beyond the Galactic center at distances
of more than 9 kiloparsec from the Sun. These regions are opaque at optical wavelengths
because of absorption by interstellar dust, and distances are very large and hard to measure.
We report a direct trigonometric parallax distance of 20:4þ2:8
2:2 kiloparsec obtained with the Very
Long Baseline Array to a water maser source in a region of active star formation. These
measurements allow us to shed light on Galactic spiral structure by locating the ScutumCentaurus
spiral arm as it passes through the far side of the Milky Way and to validate a
kinematic method for determining distances in this region on the basis of transverse motions.
This document discusses three approaches to adding antennas to the GMRT array to obtain denser uv coverage and a better signal-to-noise ratio. Approach 1 involves adding a single antenna and solving an equation to determine its coordinates but was found to not have a unique solution. Approach 2 adds antennas in a rectangular patch and simulates the coverage, selecting a set of three antennas. Approach 3 visually analyzes coverage from adding antennas individually at grid points in the patch, selecting a combination of three grids. The combination from Approach 3 agreed with locations from Approach 2.
Towards the identification of the primary particle nature by the radiodetecti...Ahmed Ammar Rebai PhD
This document summarizes a study using the CODALEMA experiment to analyze radio signals from air showers and identify properties of primary cosmic ray particles. It describes:
1) Analyzing time delays of radio signals compared to a plane wavefront hypothesis and finding systematic deviations, indicating the wavefront is curved.
2) Developing a model to reconstruct the emission center position based on fitting time delays to a parabolic function dependent on curvature radius and antenna distances.
3) Applying the model to 450 selected CODALEMA events and comparing reconstructed shower core positions to results from other models, finding consistency.
1) Lunar Orbiter tracking data revealed large mass concentrations (mascons) beneath the lunar maria.
2) The largest mascons were found beneath Mare Imbrium, Mare Serenitatis, Mare Crisium, Mare Humorum, and Mare Nectaris.
3) The mascons suggest a relationship between the formation of the maria and large impact events on the lunar surface.
Water vapour absorption in the clear atmosphere of a Neptune-sized exoplanetGOASA
1) The transmission spectrum of the exoplanet HAT-P-11b was observed using Hubble and Spitzer space telescopes.
2) Water vapor absorption was detected at 1.4 micrometers in the atmosphere, indicating a clear atmosphere down to 1 mbar pressure.
3) The detection of water vapor and relatively large atmospheric scale height places an upper limit on the abundance of heavy elements in the atmosphere of around 700 times the solar value, consistent with core accretion planet formation theories.
This document discusses orbital mechanics concepts including:
1) Calculating orbital parameters like velocity and period for satellites in circular orbits between 322-1400 km altitude.
2) Designing an observation satellite orbit with a 4 hour period to pass directly over a ground station every 4 hours at an elevation angle above 10 degrees.
3) Computing the true anomaly of a satellite in an elliptical orbit with eccentricity 0.15 and semi-major axis of 9000 km at a height of 2000 km.
4) Determining the velocities of satellites in both circular and elliptical orbits at the same orbital radius.
5) Relating the orbital periods of two satellites with semi-major axes of 18000 km
The document provides solutions to problems related to satellite systems and components. It includes:
1) Calculations of telemetry frame transmission time, maximum propagation delay, and solar cell efficiencies for a geostationary communications satellite.
2) Estimates of the area, height, and power output of solar cells on a spinner satellite.
3) Calculations of the size and area of solar sails or cells needed to power different geostationary satellite designs.
4) Determinations of battery capacity and weight for a direct broadcast TV satellite.
5) Calculations of antenna diameters, beamwidths, and gains for satellites using Ku and Ka band frequencies.
6) Estimates of antenna dimensions and
The bright optical_flash_and_afterglow_from_the_gamma_ray_burst_grb_130427aSérgio Sacani
1) Researchers observed an optical flash and fading afterglow from the powerful gamma-ray burst GRB 130427A. 2) The optical and gamma-ray (>100 MeV) light curves were closely correlated during the first 7,000 seconds, best explained by reverse shock emission generated in the relativistic ejecta. 3) At later times, the optical light showed evidence of forward shock emission as it interacted with the surrounding environment.
MODELLING AND ATMOSPHERIC ERRORS IN GPS SIGNAL PROPAGATIONSHADABANSARI57
A BRIEF INTRODUCTION TO IONOSPHERIC AND TROPOSPHERIC ERRORS IN GPS SIGNAL PROPAGATION
DERIVATION OF FORMULA WITH THE BASIC LEVEL.
BASIC UNDERSTANDING OF FIGURE..
FOLLOW THE REFERENCE BOOK FOR MORE DETAIL.
IOSR Journal of Applied Physics (IOSR-JAP) is an open access international journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
This document contains solutions to 5 questions about orbital mechanics. Question 1 calculates the centripetal and centrifugal accelerations, velocity, and orbital period of a satellite in a 1,400 km circular orbit. Question 2 does similar calculations for a 322 km circular orbit, finding the orbital angular velocity, period, and velocity. Question 3 calculates Doppler shifts for signals from this satellite received by observers in space and on the Earth's surface. Question 4 states Kepler's laws of planetary motion and uses the third law to find the orbital period of a satellite in an elliptical orbit with a 39,152 km apogee and 500 km perigee.
Using observations from the Very Large Telescope, astronomers have discovered a dense gas cloud approximately three times the mass of Earth that is falling towards the supermassive black hole at the center of the Milky Way. The cloud is on a highly eccentric orbit that will bring it as close as 3,100 times the event horizon of the black hole in 2013. Over the past three years, the cloud has begun to disrupt due to tidal shearing from the black hole's gravitational forces, and its dynamic evolution over the next few years will provide insights into the black hole's accretion processes.
Towards the identification of the primary particle nature by the radiodetecti...Ahmed Ammar Rebai PhD
To contact the author use ahmed.rebai2@gmail.com
Radio signal from extensive air showers EAS studied by the CODALEMA experiment have been detected by means of the classic short fat antennas array working in a slave trigger mode by a particle scintillator array. It is shown that the radio shower wavefront is curved with respect to the plane wavefront hypothesis. Then a new fitting model (parabolic model) is proposed to fit the radio signal time delay distributions in an event-by-event basis. This model take into account this wavefront property and several shower geometry parameters such as: the existence of an apparent localised radio-emission source located at a distance Rc from the antenna array of and the
radio shower core on the ground. Comparison of the outputs from this model and other reconstruction models used in the same experiment show: 1)- That the radio shower core is shifted from the particle shower core in a statistic analysis approach. 2)- The capability of the radiodetection method to reconstruct the curvature radius
with a statistical error less than 50 g.cm−2 . Finally a preliminary study of the primary particle nature has been performed based on a comparison between data and Xmax distribution from Aires Monte-Carlo simulations for the same set of events.
1) The document reports on phase-resolved emission spectroscopy observations of the exoplanet WASP-43b using the Hubble Space Telescope.
2) The observations tracked the planet over three full orbits and measured its thermal emission as a function of orbital phase, allowing the researchers to construct a map of the planet's atmospheric thermal structure.
3) The results found large day-night temperature variations at all measured altitudes, with temperature monotonically decreasing with increasing pressure. A low Bond albedo of 0.07-0.18 and offset of the hottest point from the substellar point were also derived.
A new universal formula for atoms, planets, and galaxiesIOSR Journals
In this paper a new universal formula about the rotation velocity distribution of atoms, planets, and galaxies is presented. It is based on a new general formula based on the relativistic Schwarzschild/Minkowski metric, where it has been possible to obtain expressions for the rotation velocity - and mass distribution versus the distance to the atomic nucleus, planet system centre, and galactic centre. A mathematical proof of this new formula is also given. This formula is divided into a Keplerian(general relativity)-and a relativistic(special relativity) part. For the atomic-and planet systems the Keplerian distribution is followed, which is also in accordance with observations.
According to the rotation velocity distribution of the galaxies the rotation velocity increases very rapidly from the centre and reaches a plateau which is constant out to a great distance from the centre. This is in accordance with observations and is also in accordance with the main structure of rotation velocity versus distance from different galaxy measurements.
Computer simulations were also performed to establish and verify the rotation velocity distributions in the atomic – planetary- and galaxy system, according to this paper. These computer simulations are in accordance with observations in two and three dimensions. It was also possible to study the matching percentage in these calculations showing a much higher matching percentage between theoretical and observational values by this new formula.
Correction of ionospheric distortions in low frequency interferometric SAR da...grssieee
This document discusses methods for correcting distortions caused by the ionosphere in low frequency synthetic aperture radar (SAR) interferometric data. The ionosphere can cause displacement and defocusing in SAR images. The authors propose estimating the total electron content (TEC) and its spatial variation to model ionospheric distortions. They develop approaches using full-band and sub-band interferograms to estimate azimuth shifts and correct for ionospheric phase screens. Simulation results demonstrate the effectiveness of their correction methods, especially when using multiple sub-bands and increasing the number of looks, though this reduces spatial resolution. The authors conclude sub-band methods provide finer structure of the ionosphere compared to full-band approaches.
Science Express Paper by: Kevin B. Stevenson et al.GOASA
- Spectroscopic phase curve observations of the exoplanet WASP-43b using the Hubble Space Telescope revealed a distinct increase in flux as the dayside rotated into view, peaking prior to secondary eclipse.
- Analysis of the spectrally resolved phase curves showed wavelength-dependent amplitudes, phase shifts, and eclipse depths, allowing inference of the temperature structure and molecular abundances at 15 orbital phases.
- Atmospheric modeling found water to be the dominant absorber influencing the phase-resolved emission spectra. The data showed large day-night temperature variations at all measured altitudes and a monotonically decreasing temperature with pressure.
Optimal trajectory to Saturn in ion-thruster powered spacecraftKristopherKerames
In this document, I derive the equations of motion for an ion-thruster powered spacecraft and use numerical methods to calculate its optimal trajectory to Saturn. I did this work within 48 hours for the University Physics Competition in 2020.
Dissecting x ray_emitting_gas_around_the_center_of_our_galaxySérgio Sacani
1) The Chandra X-ray Observatory was used to observe the supermassive black hole at the center of the Milky Way, Sgr A*, for a total of 3 megaseconds.
2) The observations revealed extended X-ray emission around Sgr A* that aligns spatially with a surrounding disk of massive stars.
3) Spectral analysis ruled out low-mass stars as the origin of the X-ray emission and instead found evidence that the emission is from a radiatively inefficient accretion flow onto the black hole, with an outflow present.
Investigating Techniques to Model the Martian Surface UsingAlexander Reedy
1) The document describes techniques to model the Martian surface using principal component analysis and target transformation in order to isolate cloud spectral signatures from surface signatures.
2) It analyzes data from 1994-1995 using three methods - binning, k-means clustering, and picking vertices - to recover spectral endmembers from the target transformations.
3) It finds that picking the vertices method most consistently provides endmembers with good brightness ranges and distinct spectral shapes over both Martian oppositions, making it the best technique for modeling the Martian surface and isolating cloud signals.
This document outlines research on using aerodynamic drag to stabilize spacecraft attitude and target re-entry locations. Key points:
- A Drag De-Orbit Device (D3) is proposed that can be attached to CubeSats to control drag and expedite deorbiting. It has retractable tape spring booms to modulate drag area.
- Algorithms are presented for guidance trajectory generation, navigation with Kalman filtering, and guidance tracking. The algorithms compute drag profiles to guide a spacecraft along a trajectory to re-enter over a desired location.
- Hardware and simulation results show the D3 provides passive attitude stability and the algorithms can target re-entry points. Future work involves testing the D3
A close pair_binary_in_a_distant_triple_supermassive_black_hole_systemSérgio Sacani
This document reports the discovery of a triple supermassive black hole system through radio observations. Very Long Baseline Interferometry observations revealed two flat-spectrum radio cores, labelled J1502SE and J1502SW, within the galaxy J1502S, separated by about 140 parsecs. Analysis of archival data provides further evidence of this close black hole pair through the detection of 'S-shaped' radio emission between the two cores, indicative of jet precession caused by the binary black holes. This is the closest black hole pair yet discovered and demonstrates a new method for finding binary black holes that cannot be spatially resolved with current instruments.
Evidence of a plume on Europa from Galileo magnetic and plasma wave signaturesSérgio Sacani
The icy surface of Jupiter’s moon, Europa, is thought to lie
on top of a global ocean1–4. Signatures in some Hubble Space
Telescope images have been associated with putative water
plumes rising above Europa’s surface5,6, providing support for
the ocean theory. However, all telescopic detections reported
were made at the limit of sensitivity of the data5–7
, thereby calling
for a search for plume signatures in in-situ measurements.
Here, we report in-situ evidence of a plume on Europa from
the magnetic field and plasma wave observations acquired on
Galileo’s closest encounter with the moon. During this flyby,
which dropped below 400 km altitude, the magnetometer8
recorded an approximately 1,000-kilometre-scale field rotation
and a decrease of over 200 nT in field magnitude, and
the Plasma Wave Spectrometer9 registered intense localized
wave emissions indicative of a brief but substantial increase
in plasma density. We show that the location, duration and
variations of the magnetic field and plasma wave measurements
are consistent with the interaction of Jupiter’s corotating
plasma with Europa if a plume with characteristics inferred
from Hubble images were erupting from the region of Europa’s
thermal anomalies. These results provide strong independent
evidence of the presence of plumes at Europa.
Waypoint Global provides staffing and consultancy services across various industries including shipping, maritime, marine, and subsea. They source both permanent and contract candidates globally to meet client needs. Their dedicated teams have deep expertise in technical roles and can advise on industry trends, regulations, and salaries. Waypoint Global aims to exceed client expectations through professional, compliant, and customized recruitment solutions.
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This document discusses orbital mechanics concepts including:
1) Calculating orbital parameters like velocity and period for satellites in circular orbits between 322-1400 km altitude.
2) Designing an observation satellite orbit with a 4 hour period to pass directly over a ground station every 4 hours at an elevation angle above 10 degrees.
3) Computing the true anomaly of a satellite in an elliptical orbit with eccentricity 0.15 and semi-major axis of 9000 km at a height of 2000 km.
4) Determining the velocities of satellites in both circular and elliptical orbits at the same orbital radius.
5) Relating the orbital periods of two satellites with semi-major axes of 18000 km
The document provides solutions to problems related to satellite systems and components. It includes:
1) Calculations of telemetry frame transmission time, maximum propagation delay, and solar cell efficiencies for a geostationary communications satellite.
2) Estimates of the area, height, and power output of solar cells on a spinner satellite.
3) Calculations of the size and area of solar sails or cells needed to power different geostationary satellite designs.
4) Determinations of battery capacity and weight for a direct broadcast TV satellite.
5) Calculations of antenna diameters, beamwidths, and gains for satellites using Ku and Ka band frequencies.
6) Estimates of antenna dimensions and
The bright optical_flash_and_afterglow_from_the_gamma_ray_burst_grb_130427aSérgio Sacani
1) Researchers observed an optical flash and fading afterglow from the powerful gamma-ray burst GRB 130427A. 2) The optical and gamma-ray (>100 MeV) light curves were closely correlated during the first 7,000 seconds, best explained by reverse shock emission generated in the relativistic ejecta. 3) At later times, the optical light showed evidence of forward shock emission as it interacted with the surrounding environment.
MODELLING AND ATMOSPHERIC ERRORS IN GPS SIGNAL PROPAGATIONSHADABANSARI57
A BRIEF INTRODUCTION TO IONOSPHERIC AND TROPOSPHERIC ERRORS IN GPS SIGNAL PROPAGATION
DERIVATION OF FORMULA WITH THE BASIC LEVEL.
BASIC UNDERSTANDING OF FIGURE..
FOLLOW THE REFERENCE BOOK FOR MORE DETAIL.
IOSR Journal of Applied Physics (IOSR-JAP) is an open access international journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
This document contains solutions to 5 questions about orbital mechanics. Question 1 calculates the centripetal and centrifugal accelerations, velocity, and orbital period of a satellite in a 1,400 km circular orbit. Question 2 does similar calculations for a 322 km circular orbit, finding the orbital angular velocity, period, and velocity. Question 3 calculates Doppler shifts for signals from this satellite received by observers in space and on the Earth's surface. Question 4 states Kepler's laws of planetary motion and uses the third law to find the orbital period of a satellite in an elliptical orbit with a 39,152 km apogee and 500 km perigee.
Using observations from the Very Large Telescope, astronomers have discovered a dense gas cloud approximately three times the mass of Earth that is falling towards the supermassive black hole at the center of the Milky Way. The cloud is on a highly eccentric orbit that will bring it as close as 3,100 times the event horizon of the black hole in 2013. Over the past three years, the cloud has begun to disrupt due to tidal shearing from the black hole's gravitational forces, and its dynamic evolution over the next few years will provide insights into the black hole's accretion processes.
Towards the identification of the primary particle nature by the radiodetecti...Ahmed Ammar Rebai PhD
To contact the author use ahmed.rebai2@gmail.com
Radio signal from extensive air showers EAS studied by the CODALEMA experiment have been detected by means of the classic short fat antennas array working in a slave trigger mode by a particle scintillator array. It is shown that the radio shower wavefront is curved with respect to the plane wavefront hypothesis. Then a new fitting model (parabolic model) is proposed to fit the radio signal time delay distributions in an event-by-event basis. This model take into account this wavefront property and several shower geometry parameters such as: the existence of an apparent localised radio-emission source located at a distance Rc from the antenna array of and the
radio shower core on the ground. Comparison of the outputs from this model and other reconstruction models used in the same experiment show: 1)- That the radio shower core is shifted from the particle shower core in a statistic analysis approach. 2)- The capability of the radiodetection method to reconstruct the curvature radius
with a statistical error less than 50 g.cm−2 . Finally a preliminary study of the primary particle nature has been performed based on a comparison between data and Xmax distribution from Aires Monte-Carlo simulations for the same set of events.
1) The document reports on phase-resolved emission spectroscopy observations of the exoplanet WASP-43b using the Hubble Space Telescope.
2) The observations tracked the planet over three full orbits and measured its thermal emission as a function of orbital phase, allowing the researchers to construct a map of the planet's atmospheric thermal structure.
3) The results found large day-night temperature variations at all measured altitudes, with temperature monotonically decreasing with increasing pressure. A low Bond albedo of 0.07-0.18 and offset of the hottest point from the substellar point were also derived.
A new universal formula for atoms, planets, and galaxiesIOSR Journals
In this paper a new universal formula about the rotation velocity distribution of atoms, planets, and galaxies is presented. It is based on a new general formula based on the relativistic Schwarzschild/Minkowski metric, where it has been possible to obtain expressions for the rotation velocity - and mass distribution versus the distance to the atomic nucleus, planet system centre, and galactic centre. A mathematical proof of this new formula is also given. This formula is divided into a Keplerian(general relativity)-and a relativistic(special relativity) part. For the atomic-and planet systems the Keplerian distribution is followed, which is also in accordance with observations.
According to the rotation velocity distribution of the galaxies the rotation velocity increases very rapidly from the centre and reaches a plateau which is constant out to a great distance from the centre. This is in accordance with observations and is also in accordance with the main structure of rotation velocity versus distance from different galaxy measurements.
Computer simulations were also performed to establish and verify the rotation velocity distributions in the atomic – planetary- and galaxy system, according to this paper. These computer simulations are in accordance with observations in two and three dimensions. It was also possible to study the matching percentage in these calculations showing a much higher matching percentage between theoretical and observational values by this new formula.
Correction of ionospheric distortions in low frequency interferometric SAR da...grssieee
This document discusses methods for correcting distortions caused by the ionosphere in low frequency synthetic aperture radar (SAR) interferometric data. The ionosphere can cause displacement and defocusing in SAR images. The authors propose estimating the total electron content (TEC) and its spatial variation to model ionospheric distortions. They develop approaches using full-band and sub-band interferograms to estimate azimuth shifts and correct for ionospheric phase screens. Simulation results demonstrate the effectiveness of their correction methods, especially when using multiple sub-bands and increasing the number of looks, though this reduces spatial resolution. The authors conclude sub-band methods provide finer structure of the ionosphere compared to full-band approaches.
Science Express Paper by: Kevin B. Stevenson et al.GOASA
- Spectroscopic phase curve observations of the exoplanet WASP-43b using the Hubble Space Telescope revealed a distinct increase in flux as the dayside rotated into view, peaking prior to secondary eclipse.
- Analysis of the spectrally resolved phase curves showed wavelength-dependent amplitudes, phase shifts, and eclipse depths, allowing inference of the temperature structure and molecular abundances at 15 orbital phases.
- Atmospheric modeling found water to be the dominant absorber influencing the phase-resolved emission spectra. The data showed large day-night temperature variations at all measured altitudes and a monotonically decreasing temperature with pressure.
Optimal trajectory to Saturn in ion-thruster powered spacecraftKristopherKerames
In this document, I derive the equations of motion for an ion-thruster powered spacecraft and use numerical methods to calculate its optimal trajectory to Saturn. I did this work within 48 hours for the University Physics Competition in 2020.
Dissecting x ray_emitting_gas_around_the_center_of_our_galaxySérgio Sacani
1) The Chandra X-ray Observatory was used to observe the supermassive black hole at the center of the Milky Way, Sgr A*, for a total of 3 megaseconds.
2) The observations revealed extended X-ray emission around Sgr A* that aligns spatially with a surrounding disk of massive stars.
3) Spectral analysis ruled out low-mass stars as the origin of the X-ray emission and instead found evidence that the emission is from a radiatively inefficient accretion flow onto the black hole, with an outflow present.
Investigating Techniques to Model the Martian Surface UsingAlexander Reedy
1) The document describes techniques to model the Martian surface using principal component analysis and target transformation in order to isolate cloud spectral signatures from surface signatures.
2) It analyzes data from 1994-1995 using three methods - binning, k-means clustering, and picking vertices - to recover spectral endmembers from the target transformations.
3) It finds that picking the vertices method most consistently provides endmembers with good brightness ranges and distinct spectral shapes over both Martian oppositions, making it the best technique for modeling the Martian surface and isolating cloud signals.
This document outlines research on using aerodynamic drag to stabilize spacecraft attitude and target re-entry locations. Key points:
- A Drag De-Orbit Device (D3) is proposed that can be attached to CubeSats to control drag and expedite deorbiting. It has retractable tape spring booms to modulate drag area.
- Algorithms are presented for guidance trajectory generation, navigation with Kalman filtering, and guidance tracking. The algorithms compute drag profiles to guide a spacecraft along a trajectory to re-enter over a desired location.
- Hardware and simulation results show the D3 provides passive attitude stability and the algorithms can target re-entry points. Future work involves testing the D3
A close pair_binary_in_a_distant_triple_supermassive_black_hole_systemSérgio Sacani
This document reports the discovery of a triple supermassive black hole system through radio observations. Very Long Baseline Interferometry observations revealed two flat-spectrum radio cores, labelled J1502SE and J1502SW, within the galaxy J1502S, separated by about 140 parsecs. Analysis of archival data provides further evidence of this close black hole pair through the detection of 'S-shaped' radio emission between the two cores, indicative of jet precession caused by the binary black holes. This is the closest black hole pair yet discovered and demonstrates a new method for finding binary black holes that cannot be spatially resolved with current instruments.
Evidence of a plume on Europa from Galileo magnetic and plasma wave signaturesSérgio Sacani
The icy surface of Jupiter’s moon, Europa, is thought to lie
on top of a global ocean1–4. Signatures in some Hubble Space
Telescope images have been associated with putative water
plumes rising above Europa’s surface5,6, providing support for
the ocean theory. However, all telescopic detections reported
were made at the limit of sensitivity of the data5–7
, thereby calling
for a search for plume signatures in in-situ measurements.
Here, we report in-situ evidence of a plume on Europa from
the magnetic field and plasma wave observations acquired on
Galileo’s closest encounter with the moon. During this flyby,
which dropped below 400 km altitude, the magnetometer8
recorded an approximately 1,000-kilometre-scale field rotation
and a decrease of over 200 nT in field magnitude, and
the Plasma Wave Spectrometer9 registered intense localized
wave emissions indicative of a brief but substantial increase
in plasma density. We show that the location, duration and
variations of the magnetic field and plasma wave measurements
are consistent with the interaction of Jupiter’s corotating
plasma with Europa if a plume with characteristics inferred
from Hubble images were erupting from the region of Europa’s
thermal anomalies. These results provide strong independent
evidence of the presence of plumes at Europa.
Waypoint Global provides staffing and consultancy services across various industries including shipping, maritime, marine, and subsea. They source both permanent and contract candidates globally to meet client needs. Their dedicated teams have deep expertise in technical roles and can advise on industry trends, regulations, and salaries. Waypoint Global aims to exceed client expectations through professional, compliant, and customized recruitment solutions.
#SolParaTodos trata-se do programa de indicações da Surya Solar. Qualquer pessoa pode indicar clientes e ganhar dinheiro com isso.
Se você conhece alguma pessoa ou empresa que possa se interessar em instalar energia elétrica solar, indique para nós!
Ganha todo mundo, ganha quem indica (dinheiro) e ganha quem for indicado (desconto).
Simples, fácil e sem burocracia!
SB Engineers is a leading manufacturer and supplier of material handling equipment such as overhead cranes, wire rope hoists, gantry cranes, jib cranes, under slung cranes, winches, and goods lifts. The company was established in 2009 by Suresh Patel with a vision to be the most successful and respected crane manufacturer through high quality products. SB Engineers is committed to providing technologically superior products and high quality services to achieve total customer satisfaction.
Internet marketing is essential to the marketing mix. Even the business on the corner need to be marketing on the internet. With internet marketing, small companies now have the resources to perform sales and that is why business owners are streamlining their internet marketing.
Contact us for free web marketing consultation at info@matictechnology.com
Abdul Wahid Anwar is a warehouse supervisor and SAP administrator seeking a career that utilizes his experience and skills. He has over 15 years of experience in logistics, materials management, and SAP systems. His resume provides details on his education and qualifications, professional experiences spanning several companies in Qatar, and responsibilities in areas like warehouse operations, inventory management, and SAP administration.
Dokumen tersebut membahas tentang manajemen proses pada sistem operasi Linux. Ada empat konsep dasar manajemen proses yaitu multiprogramming, pseudoparallelism, multiprocessing, dan distributed processing. Proses memiliki ID unik dan dapat diciptakan, dihentikan, ditunda, dilanjutkan, diblokir, dibangunkan, dijadwalkan, dan berkomunikasi. Perintah-perintah dasar manajemen proses di Linux adalah ps dan kill.
This doctoral thesis investigated the role of MTH1 and MYH proteins in genotoxic effects of radiation. It used the TK6 and MCF-10A cell lines to study the effects of ultraviolet A radiation and low-dose gamma radiation exposure with and without MTH1 and MYH expression. The results showed that MTH1 protects cells from UVA-induced mutations and MTH1 and MYH cooperate to protect cells from gamma radiation-induced genotoxicity. No dose rate effect was observed for gamma radiation-induced mutations. The thesis contributes to understanding the mechanisms of radiation-induced oxidative stress and its relation to genotoxicity and cancer induction.
The document provides information on Circuit Water Engineering Equipment, a South African company that manufactures and distributes water and wastewater treatment equipment. It discusses the company's history and products. The products are used for municipal wastewater treatment, industrial water treatment, potable water treatment, and other applications like mining. Specific equipment discussed includes screens like the MEVA Rotoscreen, Monoscreen, and Multi Rake Screen. It also mentions grit removal equipment, conveyors, and other products.
The document summarizes research to create a new catalog of intermediate velocity clouds using the Leiden/Argentina/Bonn Galactic HI survey. Researchers are fitting Gaussian curves to spectra from the survey to identify clouds based on their velocity. Each fit is reviewed manually given limitations of automated fitting. Preliminary results examining 45,000 spectra show evidence of compact intermediate clouds and correlations between velocity and density in large cloud complexes. Future work will compare the full sky catalog to previous work and models of gas flows in the Milky Way.
This document summarizes Edwin Hubble's 1929 paper establishing a relationship between the distance and radial velocity of extragalactic nebulae. Hubble analyzed spectra and distances of 24 nebulae, finding a linear correlation between higher distances and velocities after correcting for solar motion. Hubble proposed a new solution where velocity varies directly with distance, with a velocity increase of around 500 km/sec per million parsecs. This relationship was supported by data from 22 additional nebulae. The findings helped establish the expanding universe model and Hubble's law relating galaxy recession velocity and distance.
The document discusses the Robertson-Walker metric and its application to cosmological redshifts. It contains the following key points:
1. The Robertson-Walker metric describes a homogeneous and isotropic universe and can account for the observed redshift of distant galaxies by considering the expansion of the universe over time.
2. The metric allows for spaces with positive, negative, or zero curvature, corresponding to closed, open, or flat geometries for the universe.
3. Application of the metric successfully explains Hubble's observation of redshift proportional to distance as being due to the Doppler effect from the receding motion of galaxies caused by the expansion of the universe.
1) Researchers observed 15 transits of the exoplanet GJ 1214b using the Hubble Space Telescope to measure its transmission spectrum from 1.1 to 1.7 microns.
2) The transmission spectrum was featureless, inconsistent with cloud-free atmospheres dominated by water, methane, carbon monoxide, nitrogen, or carbon dioxide.
3) The most likely explanation for the featureless spectrum is the presence of high-altitude clouds in the planet's atmosphere, which block the transmission of stellar light through the lower atmosphere.
Determination of Milky Way Rotation Curve Through Observation of Redshift of ...Daniel Bulhosa Solórzano
This experiment used a radio telescope to measure the rotation curve of the Milky Way galaxy by observing the redshift of hydrogen radiation at 1420.40 MHz. Measurements were taken at galactic longitudes from 5 to 90 degrees. The results showed reasonable agreement with published values for radii greater than 3 kpc. However, considering the mass contained within 8.33 kpc as suggested by the rotation curve reveals a discrepancy, with more mass implied than can be accounted for by observed matter, suggesting the presence of unseen "dark matter".
Propagation of highly_efficient_star_formation_in_ngc7000Sérgio Sacani
This document summarizes a study of star formation in molecular clouds near the H II region NGC 7000. The authors surveyed NH3 and H2O maser emission toward the molecular cloud L935 located near NGC 7000. They identified five dense molecular clumps based on NH3 emission, which have similar gas temperatures but different levels of star formation activity. One clump located near the boundary of the H II region has a high star formation efficiency of 36-62%, suggesting triggered star formation due to its interaction with the expanding H II region.
Results from telescope_array_experimentSérgio Sacani
The Telescope Array (TA) experiment studies ultrahigh energy cosmic rays using a hybrid detector consisting of a surface detector and three fluorescence detector stations. This paper reports three results from TA:
1) The cosmic ray spectrum measured by the surface detector shows an ankle feature and a 3.5 sigma suppression at the expected GZK cutoff energy, consistent with the HiRes experiment.
2) Measurement of the average shower maximum depth with the fluorescence detectors indicates a light composition, most likely protons.
3) A search for correlations between surface detector events and Active Galactic Nuclei found no significant correlations, consistent with results from HiRes.
1) High-dispersion spectroscopy was used to observe the young exoplanet Beta Pictoris b, detecting a blueshifted radial velocity of -15±1.7 km/s and rotational broadening of 25±3 km/s, indicating it spins faster than any planet in the solar system.
2) Beta Pictoris b's high spin velocity is consistent with an extrapolation of the trend of increasing spin velocity with planet mass seen in the solar system.
3) At an estimated age of 11±5 Myr, Beta Pictoris b is expected to cool and shrink over time, which would cause it to spin up further to a rotation velocity of around 40 km/s.
Polarized reflected light from the Spica binary systemSérgio Sacani
Close binary systems often show linear polarization varying
over the binary period, usually attributed to light scattered
from electrons in circumstellar clouds1–3
. One of the brightest
close binary systems is Spica (alpha Virginis) consisting of
two B-type stars orbiting with a period of just over four days.
Past observations of Spica have shown low polarization with
no evidence for variability4–6. Here we report new high-precision polarization observations of Spica that show variation
with an amplitude of about 200 parts per million. By including
polarized radiative transfer in a binary star model, we show
that the phase-dependent polarization is mainly due to light
reflected from the primary component of the binary system
off the secondary component and vice versa. The stars reflect
only a few per cent of the incident light, but the reflected light
is very highly polarized. The polarization results show that the
binary orbit is clockwise and the position angle of the line of
nodes is 130.4° ± 6.8°, in agreement with intensity interferometer results7
. We suggest that reflected light polarization
may be much more important in binary systems than has previously been recognized and may be a way of detecting previously unrecognized close binaries.
Water vapour absorption_in_the_clear_atmosphere_of_a_neptune_sized_exoplanetSérgio Sacani
This document summarizes research on the transmission spectrum of the exoplanet HAT-P-11b, a Neptune-sized planet. Observations from the Hubble Space Telescope and Spitzer Space Telescope detected water vapor absorption in the planet's atmosphere at a wavelength of 1.4 micrometers. Analysis of the spectrum indicates the atmosphere is predominantly clear down to 1 mbar and has a hydrogen abundance similar to solar values. Atmospheric modeling suggests a metallicity around 190 times that of the Sun's, in agreement with core accretion planet formation theories. This makes HAT-P-11b the smallest exoplanet to date with a detected molecular signature in its atmosphere, providing new insights into the composition and formation of Neptune-sized
This document summarizes a paper that presents models for locations and motions in the solar system. Ratios of orbital angular velocities are shown for planets and moons, with common ratios around 2.5 that may relate to an L-frequency. A generalized elliptic orbit model is derived, giving angular velocity as a function of eccentricity and L-frequency. Frequency ratios found in musical instruments and the northern lights are also discussed. Preliminary models for fractal locations using an iteration formula producing a Julia set are presented.
Students aged 12 to 18 observed the Big Bang using an 11-inch telescope. They measured redshifts of galaxies and deduced quantitative conclusions about the age of the universe and density of dark matter. Key findings included:
- Measuring significant redshifts of 0.0077 and 0.003 for galaxies NGC 3516 and M66, matching literature values.
- Interpreting the main emission line at 6590 Angstroms as hydrogen-alpha, indicating a redshift of 0.0077 for NGC 3516.
- Concluding the Big Bang observations were highly significant based on statistical analysis, despite limitations of the small telescope.
Discovery of rotational modulations in the planetary mass companion 2m1207b i...Sérgio Sacani
Rotational modulations of brown dwarfs have recently provided powerful constraints on the properties
of ultra-cool atmospheres, including longitudinal and vertical cloud structures and cloud evolution.
Furthermore, periodic light curves directly probe the rotational periods of ultra-cool objects. We
present here, for the first time, time-resolved high-precision photometric measurements of a planetarymass
companion, 2M1207b. We observed the binary system with HST/WFC3 in two bands and with
two spacecraft roll angles. Using point spread function-based photometry, we reach a nearly photonnoise
limited accuracy for both the primary and the secondary. While the primary is consistent with
a flat light curve, the secondary shows modulations that are clearly detected in the combined light
curve as well as in di↵erent subsets of the data. The amplitudes are 1.36% in the F125W and 0.78%
in the F160W filters, respectively. By fitting sine waves to the light curves, we find a consistent period
of 10.7+1.2
−0.6 hours and similar phases in both bands. The J- and H-band amplitude ratio of 2M1207b
is very similar to a field brown dwarf that has identical spectral type but di↵erent J-H color. Importantly,
our study also measures, for the first time, the rotation period for a directly imaged extra-solar
planetary-mass companion.
Uma equipe de astrônomos norte-americanos descobriu o par de buracos negros supermassivos mais próximos até agora no universo.
O par de buracos negros está localizado no centro do quasar chamado de PKS 1302-102, a aproximadamente 3.5 bilhões de anos-luz de distância.
Esses dois buracos negros estão separados de apenas uma semana-luz e estão num movimento espiral um em direção ao outro que deve acabar com uma colisão cataclísmica.
Em contraste, o par de buracos negros mais próximos descoberto até então estava separado de aproximadamente 20 anos-luz.
SPECTROSCOPIC CONFIRMATION OF THE EXISTENCE OF LARGE, DIFFUSE GALAXIES IN THE...Sérgio Sacani
We recently identified a population of low surface brightness objects in the field of the z = 0.023 Coma cluster,
using the Dragonfly Telephoto Array. Here we present Keck spectroscopy of one of the largest of these “ultradiffuse
galaxies” (UDGs), confirming that it is a member of the cluster. The galaxy has prominent absorption
features, including the Ca II H+K lines and the G-band, and no detected emission lines. Its radial velocity of
cz=6280±120 km s−1 is within the 1σ velocity dispersion of the Coma cluster. The galaxy has an effective
radius of 4.3 ± 0.3 kpc and a Sérsic index of 0.89 ± 0.06, as measured from Keck imaging. We find no indications
of tidal tails or other distortions, at least out to a radius of ∼2re. We show that UDGs are located in a previously
sparsely populated region of the size—magnitude plane of quiescent stellar systems, as they are ∼6 mag fainter
than normal early-type galaxies of the same size. It appears that the luminosity distribution of large quiescent
galaxies is not continuous, although this could largely be due to selection effects. Dynamical measurements are
needed to determine whether the dark matter halos of UDGs are similar to those of galaxies with the same
luminosity or to those of galaxies with the same size.
This document summarizes cosmological parameters measured from galaxy surveys. It discusses:
1) Direct measurements of the Hubble constant from the Hubble Space Telescope and Planck, finding values of 72-74 km/s/Mpc and 67.3 km/s/Mpc respectively.
2) Supernova surveys finding evidence for an accelerating universe with matter density of ~30% and dark energy density of ~70%.
3) Measurements of cosmic microwave background from COBE, WMAP and Planck, determining ages and densities of the universe.
4) Galaxy clustering surveys like SDSS detecting baryon acoustic oscillations to measure dark energy properties.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
This document reports the discovery of a newly discovered optical Einstein ring (ER) called the "Canarias Einstein Ring". It was discovered serendipitously in imaging data from the Dark Energy Camera. Follow-up spectroscopy with the Gran Telescopio CANARIAS confirmed the nature of the system, with the lens being an early-type galaxy at a redshift of z=0.581 and the source being a starburst galaxy at z=1.165. Analysis of the system determined the Einstein radius to be 2.16 arcseconds and the total enclosed mass producing the lensing effect to be 1.86 ± 0.23 × 1012 solar masses.
This document provides information about alpha decay and alpha particles. It discusses:
1) Unstable nuclei attain stability through emission of alpha particles, which are made up of 2 protons and 2 neutrons.
2) Alpha decay involves the emission of an alpha particle from an unstable nucleus, leaving a lighter nucleus. Conservation laws apply.
3) The range of alpha particles is very small, usually only a few centimeters in air or solid materials, due to their high ionization which causes energy loss. Their short range makes them easily stopped.
This study analyzed transit observations of the Neptune-mass exoplanet GJ 436b taken with the Hubble Space Telescope. The transmission spectrum was found to be featureless, ruling out cloud-free hydrogen-dominated atmosphere models with high significance. The flat transmission spectrum is consistent with either an atmosphere containing high-altitude clouds located at a pressure of around 1 millibar, or a relatively hydrogen-poor atmosphere with 3% hydrogen and helium by mass. Bayesian atmospheric modeling showed that cloudy hydrogen-dominated or high-metallicity hydrogen-poor atmospheres provide the best fits to the data. Further observations are needed to distinguish between these scenarios.
1. Detecting the Magellanic Stream
Report by Jonathan Kao.1
May 8, 2015
ABSTRACT
This report summarizes our attempt to detect the Magellanic Stream and
the results we obtained. The telescope we used was the 4.5m-diameter dish at
the Leuschner Observatory. The region of l = 61◦
to 110◦
and b = −30◦
to
−90◦
in galactic coordinates was observed with a 2◦
resolution, 380 profiles total.
Resulting images showed high-velocity gases of −100 to −350km/s, which we
believe were signals from the Magellanic Stream.
1. Introduction
1.1. About the Magellanic Stream
Our Milky Way Galaxy belongs to a cluster of galaxies often referred to as the Local
Group, which contains over 50 galaxies. Many of the dwarf galaxies surrounding the Milky
Way are known as the ”satellite galaxies” of the Milky Way, and among them two of the
closest to the Milky Way (visible with the naked eye) are the Large Magellanic Cloud (LMC)
and Small Magellanic Cloud (SMC). LMC and SMC are connected by a bridge of gas referred
to as the Magellanic Bridge (MBR) due to the strong tidal interaction between them, and
the two bodies travel together as a system, as shown in figure 1.
Due to the relatively short distance from the Milky Way, the tidal interaction between
the Milky Way and the Magellanic system is also significant. Some argue that this might have
caused the formation of the Magellanic Stream. Results announced in 2010 suggest that it
might have formed 2.5 billion years ago when LMC and SMC passed close to each other and
caused large-scale star formation and supernovae explosions, of which the release of energy
could have blown some gas out of the system, which then got caught by the gravitational
pull of the Milky Way and started flowing towards us.2
1
Experiments done by Team HAJ: Han Aung, Ankit Patel and Jonathan Kao.
2
Emily Baldwin, ”Giant Intergalactic Gas Streamer Gets Longer,” Astronomy Now. URL: http://
www.astronomynow.com/news/n1001/05streamer/
2. – 2 –
Fig. 1.— An illustration of LMC, SMC, MBR and the Magellanic Stream relative to
the Milky Way. Picture credit: Harvard-Smithsonian Center for Astrophysics, URL:
www.cfa.harvard.edu/news/2010-18
1.2. Challenges We Expect
We attempt to detect the stream by sampling HI signals from the hydrogen gas. Unlike
in the projects our peers have been working on, in this project we are trying to detect a
stream of gas outside of our own Milky Way Galaxy, which means that the incoming signal
from our target is extremely weak compared to other sources and can easily get dominated
by signals from other bodies within the Milky Way and any source of noise, including our
own equipments. This means we need much longer integration times for each point we
are observing, and developing programs to extract information from our data can be very
challenging. Additionally, the relative location of the Magellanic Stream to the Milky Way
makes it much more easily observable from the southern hemisphere of Earth, so the time
in a day when we can observe it is very limited.
3. – 3 –
2. Methods
2.1. The Telescope Setup
The telescope we use is the 4.5m-diameter radio dish at the Leuschner Observatory,
and we sample at 24MHz but only use 12MHz on the positive side. The received signal
goes through a series of amplifiers, band-pass filters and mixers before being integrated and
sampled. See figure 2 for a detailed block diagram of the setup.
Fig. 2.— The Telescope Setup: block diagram with filters and local oscillator frequencies
marked. Illustration by Jonathan Kao.
4. – 4 –
2.2. Taking and Analyzing the Data
In terms of galactic coordinates (l, b), the area we want to cover is a pie-shaped area
bounded by l = 60◦
to 110◦
and b = −90◦
to −30◦
, covering about 1250 square degrees. At
about 2◦
spacing, we determined the need of about 380 profiles, with an integration time of
above 10 minutes per profile. There are 31 values of b to map while the number of points for
each b varied, so we take the ”row-by-row” approach by fixing b and scanning through all
the l for that b. The pointing of the telescope is done with the provided ”follow” procedure
and the data recording using the ”leuschner rx” procedure, both in IDL.
To perform the intensity calibration, before and after taking each set of data we take
the ”noise-on datum” by turning the noise diode on. We calibrate the system by assuming
that the noise diode has temperature of 300K, and extract information about the velocity
from the data. For details on the process, refer to the report ”21-cm Line, Coax Cables and
Waveguides” by Jonathan Kao, with the major difference being using a smoothed spectrum
for calibration instead of the ratios of upper and lower sidebands.
Another piece of information we can get is the relative intensity of the HI line at each
point. The mass seen by the telescope can be represented with the formula MHI(v) =
1.8 × 1018
∆vd2
mHTAΩb (grams), where ∆v is the velocity interval, d is the distance, mH is
the mass of each HI atom, TA is the antenna temperature, and Ωb is the solid angle of the
beam. Since everything other than TA and ∆v is constant, we get MHI ∝ TA∆v, so we can
use TA∆v to represent intensity.
2.3. Creating the Image
We present our resulting map in two color images. With the goal of mapping the
expanding gas of the Magellanic Stream, we plot the data in the 3D space of (l, b, v), which
are the galactic coordinates and the measured velocity at each point. The data points are
reorganized into a grid, and the 1D image is produced using the IDL procedure ”display”
provided. Additionally, since we can get information about intensity, we plot the same data
in the 4D space of (l, b, v, I) with I being the measured intensity at each point. This 2D
image is produced using the IDL procedure ”display 2d” provided.3
3
The procedure ”display 2d” had a fixed layout for the image and the colorbar, which did not meet our
needs. We created a slightly altered version from it to create the layout we needed.
5. – 5 –
3. Results
3.1. The Spectra
Figure 3 shows an example of the resulting spectrum for a certain point. The resulting
spectrum is a sum of all the separate spectra we took for the same point. The plot on the
top shows the full spectrum with temperature plotted against velocity. We believe that the
largest peak to the right represents the signals we receive from bodies within the Milky Way,
while the smallest peak to the left could be noise or signals from other bodies. The peak
in the middle at around −140km/s was what we were looking for, so we zoom in on that
section and fit a Gaussian to the shape, as shown in the plot on the bottom. On the other
hand, figure 4 shows a bad example in which a Gaussian cannot be fitted to the spectrum.
In this case we discard the data values at the point.
Fig. 3.— ”Good Data”: this figure shows the
full spectrum at b = −90◦
and the nicely fitted
Gaussian. Plots by Han Aung.
Fig. 4.— ”Bad Data”: this figure shows the
full spectrum at l = 61◦
and b = −66◦
and the
difficulty in Gaussian fit. Plots by Han Aung.
6. – 6 –
3.2. The Images
Figures 5 and 6 shows the resulting 1D images of our data. First we note that since
the coordinates are in galactic coordinates, the more negative the b the less profiles (points),
meaning that it is a pie-shaped region. In our images we stretched it out to a rectangle,
therefore the top of the images are the least deformed while the bottom of the images are the
most stretched out. In figure 5 we can see LSR velocities ranging from around −100km/s
to −350km/s, with negative velocity meaning the HI gas we observe is traveling towards us.
In figure 6 we see that the relative intensity is higher towards the pole. Figure 7 shows the
two 1D images combined, in which we can see both of the trends.
Fig. 5.— 1D Image - Velocity: this figure
shows the LSR velocities of the gases we ob-
served. We can see higher-velocity gas clus-
tering at around b = −45◦
and the velocities
approaching 0km/s as we approach the pole
(b = −90◦
). Image by Jonathan Kao.
Fig. 6.— 1d Image - Intensity: this figure
shows the relative intensities (normalized to
a scale of 0 to 1) of the gases we observed.
We can see that the intensities are higher as
we approach the pole (b = −90). Image by
Jonathan Kao.
7. – 7 –
Fig. 7.— 2D Image: this figure shows the resulting image produced by combining the two
1D images into a 2D image. The color indicates the velocity and the brightness indicates
the relative intensity. Image by Jonathan Kao.
8. – 8 –
4. Discussion
The most important thing to ask now is whether what we detected was in fact the
Magellanic Stream. Our 1D velocity map is again shown in figure 9, and we compare with
previous studies, figure 8 shows a velocity map from a study by Fox, Andrew J. et. al.. Since
the region we covered was approximately the upper half of the map in figure 8, comparing
the velocities we can say that the results are fairly close. In both figures we see that the
highest velocities occur at around b = −40◦
to −50◦
with peak values of −350km/s or above,
and velocity approaches 0km/s as we get closer to the pole at b = −90◦
. With similar values
in velocity and similar distributions, we would argue that even though the measurements
may not be accurate, what we detected was indeed the Magellanic Stream.
Fig. 8.— Velocity Map of the Magellanic
Stream. Figure credit: Fox, Andrew J. et al.,
”Exploring the Origin and Fate of the Magel-
lanic Stream with Ultraviolet and Optical Ab-
sorption,” Astrophys.J. 718 (2010) 1046-1061.
Fig. 9.— 1D Image - Velocity: this figure
shows our 1D velocity map of the region ob-
served. It is the same as figure 5.
9. – 9 –
However, there were some problems with the data we obtained that could have made our
relative intensity map inaccurate. While the setup of the telescope at Leuschner Observatory
sampled data with x-polarization and y-polarization, for unknown reasons the y-polarization
in the data we took did not reveal any useful information regarding the HI line. Therefore
we had to use the x-polarization only for calculating the intensity, and we believe that the
results are off. This was also why we made our images using relative intensities rather than
absolute values.
Lastly we would like to discuss whether the two trends we see make sense or not. As
described in section 3, the two trends we see are ”lower velocities” and ”higher intensities”
as we get closer to the pole at b = −90◦
. If we base the discussion on the understanding
we got from the background information described in section 1.1, since the gases get caught
by the Milky Way’s gravitational pull, the older the age (age meaning how long since the
gas escaped from the Magellanic System) the higher the velocity (negative). Additionally,
we might also expect the regions closer to the Magellanic System having higher intensities.
Knowing that b = −30◦
is the furthest and b = −90◦
is the closest to the current position
of the Magellanic Clouds, it seems reasonable to see higher velocities towards the b = −30◦
end and higher intensities towards the b = −90◦
end.
5. Conclusion
There were a few things that could definitely have been improved, and a few difficulties
that could be solved under different circumstances. With the radio dish at Leuschner being
brand new (for a nice photo see figure 10), we could not be sure whether the telescope would
work as expected, and the intensity calibrations we did within this short period of time were
probably not accurate enough. Also, the signal from the Magellanic Stream was so weak
that we had to take a total of more than 60 hours of data to cover the whole region, which
meant that there were no chances to closely examine the data and retake data to replace
the bad ones. However, even though we could not say for sure that we accurately observed
the Magellanic Stream, we are proud to say that we did actually detect something from the
Stream. We could definitely make more accurate measurements if we had more time.
10. – 10 –
6. Appendix - Photos
Fig. 10.— Professor Carl Heiles with the new 4.5m-diameter dish at Leuschner Observatory.
We can see the old dish down on the ground next to the new dish. Photo by Jonathan Kao.
Fig. 11.— Team HAJ presents: a scenic shot of the famous water tank with no water at
Leuschner Observatory. Photo by Jonathan Kao.