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Diss defense
- 1. Ph.D. Dissertation Defense July 14th , 2014 Stellar Variability: A Broad and Narrow Perspective Monnier et al. 2007 J. Robert Parks Georgia State University Advisor: Russel White Committee: Peter Plavchan (IPAC) John Monnier (Umich) Fabien Baron Doug Gies Gary Hastings Hal McAlister Credit: NASA/JPL-Caltech/T. Pyle
- 2. Ph.D. Dissertation Defense July 14th , 2014 Here's hoping nobody gets beheaded during or after this talk...
- 3. Ph.D. Dissertation Defense July 14th , 2014 Types of Stellar Variability
- 4. Ph.D. Dissertation Defense July 14th , 2014 Era of High Precision Astronomy ● Photometry to parts per million, RV to m/s ● Complicates detection and characterization of exoplanets ● Complicates determination of fundamental parameters of stars ● Explores stellar interiors ● Explores stellar environments Dumusque et al. 2012 http://astro.phys.au.dk/KASC/seismology/measurements.html
- 5. Ph.D. Dissertation Defense July 14th , 2014 www.crh.noaa.gov The Broad Long temporal baseline, daily cadence photometric survey of a group of coeval stars. The Narrow High spatial resolution of a starspots on a stellar surface.
- 6. Ph.D. Dissertation Defense July 14th , 2014 ● Young stellar objects often found in chaotic environments ● Many different variability mechanism can be working concurrently ● Temporal behavior along with changes in stellar brightness and color point to variability mechanism Photometric Monitoring of Young Stars Isella (2006)
- 7. Ph.D. Dissertation Defense July 14th , 2014 ρ Ophiuchi • Well studied low mass star forming region – D ~ 125 pc, Age ~ 1 Myr • Observations – 2MASS Cal-PSWDB, 8’ x 1° FOV – 1678 star, 1582 obs. per star (JHKs) ● ~ 8 million data points – B ~ 2.5 yrs, cadence of ~ 1 day • Heavy visual extinction (Av ~ 5 to 25 mag)
- 8. Ph.D. Dissertation Defense July 14th , 2014 Cool Starspots ● Magnetic in origin ● Stellar photosphere ● Stellar colors not correlated with single band variability ● Periodic ● P < 14 days (Rebull 2001) Hot Starspots ● Accretion shock or magnetic flare ● Stellar photosphere ● Star becomes bluer as star brightens ● Periodic or aperiodic ● P < 14 days (Rebull 2001) ● TS ~ days Variable Extinction ● Circumstellar environment or intra-cloud material ● Inner disk (~1 – 3 AU) or beyond ● Star becomes redder as star dims ● Periodic or aperiodic ● P < 250 days ● TS > 50 days Variable Mass Accretion ● Circumstellar disk heats via mass transfer ● Inner Disk (~1 – 3 AU) ● Star becomes bluer as star dims ● Aperiodic ● TS ~ days to years Variability Mechanisms
- 9. Ph.D. Dissertation Defense July 14th , 2014 Cool Starspots Hot Starspots (Accretion)
- 10. Ph.D. Dissertation Defense July 14th , 2014 Extinction Accretion
- 11. Ph.D. Dissertation Defense July 14th , 2014 ● 7 point variability test ● 101 (6%) variable stars ● 72 known YSOs, 79% variable – Class I: 92% (12 of 13) – Class II: 72% (34 of 47) – Class III: 92% (11 of 12) ● 22 new candidate members ● Variable sub-categories – Periodic ● Sinusoidal-like ● Eclipse-like – Long time-scale – Irregular
- 12. Ph.D. Dissertation Defense July 14th , 2014 ● 25 stars ● Periods: 0.49 to 25.55 days ● ΔKs 0.06 to 1.64 mag, median 0.29 mag ● 3 Class I, 8 Class II, & 8 Class III ● Dominant mechansim -> cool starspots Sinusoidal-like Periodic Variables
- 13. Ph.D. Dissertation Defense July 14th , 2014 ● 6 stars; all Class II ● Periods: 2.95 to 8.00 days ● ΔKs 0.21 to 0.51 mag, median 0.31 mag ● Dominant mechansim -> extinction Eclipse-like Periodic Variables
- 14. Ph.D. Dissertation Defense July 14th , 2014 ● 31 stars ● 7 Class I, 15 Class II, & 3 Class III ● Time-scales: 64 to 790 days ● Δ Ks 0.05 to 2.31 mag, median 0.29 mag ● Dominant mechansim -> extinction/accretion Long Time-scale Variables
- 15. Ph.D. Dissertation Defense July 14th , 2014 Irregular Variables ● 40 stars ● 1 Class I, 7 Class II, & 1 Class III ● Δ Ks 0.04 to 1.11 mag, median 0.14 mag ● Dominant mechansim -> extinction/accretion
- 16. Ph.D. Dissertation Defense July 14th , 2014 ISO-Oph 126 Ps = 9.114 ± 0.090 days ΔKs = 0.06 mag Δ(HKs) = 0.10 mag Cool Starspots TS = 349 days ΔKs = 0.1 mag Δ(HKs) = 0.37 mag Extinction
- 17. Ph.D. Dissertation Defense July 14th , 2014 WL 15 Ps = 19.412 ± 0.085 days ΔKs = 0.90 mag Δ(HKs) = 0.40 mag Cool Starspots (?) TS ≥ 47 days ΔKs ~ 1 mag Δ(HKs) = 0.50 mag Extinction
- 18. Ph.D. Dissertation Defense July 14th , 2014 Ps = 5.7752 ± 0.0085 days Pe = 5.9514 ± 0.0014 days Phased to Sinusoidal Period Phased to Eclipse-like Period Δ P ~ 4 hours Distinct to 20σ level YLW 1C
- 19. Ph.D. Dissertation Defense July 14th , 2014 Potential hot proto-Jupiter ● AA Tau-like systems found in other surveys [citations] ● Driven occultations over millions of dynamical timescales ● Fundamental to understanding planet formation Sinusoidal-like Variability: Cool Starspots Eclipse-like Variability: Extinction from occulting body
- 20. Ph.D. Dissertation Defense July 14th , 2014 Huelamo et al. 2008 ● Starspots are common ● Inhibit determining stellar properties, finding planets ● Effects can be better understood if starspots could be ● spatially resolved, and ● temporally monitored Transition Slide
- 21. Ph.D. Dissertation Defense July 14th , 2014 Previous Starspot Studies Light Curve Inversion Doppler Imaging ● Indirect methods ● Rely heavily on initial assumptions ● Direct method → Long Baseline Interferometric Imaging!
- 22. Ph.D. Dissertation Defense July 14th , 2014 Primer I: UV & Aperture Synthesis van Cittert-Zernike
- 23. Ph.D. Dissertation Defense July 14th , 2014 Primer II: Visibility and Closure Phase ●Visibility → Source Distribution ● ranges from 0 to 1 ●Closure Phase →Source Asymmetry ● Ranges from -180º to 180º ● Asymmetry if non-zero or ±180º Monnier 2003
- 24. Ph.D. Dissertation Defense July 14th , 2014 Primer III: Effects of Starspots on Vis & CP ● Starspots warp “diffraction pattern” ● 180º visibility ambiguity; CP necessary to resolve
- 25. Ph.D. Dissertation Defense July 14th , 2014 λ Andromeda G8 III-IV SB1 π = 38.74 ± 0.68 mas D ~ 25 pc vsini = 6.5 km/s Pphot ~ 54 days H = 1.501 mag Δ V = 0.22 mag θ ~ 2.75 mas λ Andromeda is a bright, large, essentially single star with high amplitude photometric variability attributed to starspots.
- 26. Ph.D. Dissertation Defense July 14th , 2014 Fairborn Observatory Δ V ≤ 0.22 mag Cool starspot driven variability with P ~ 54 days 11 years Long Term Photometric Monitoring
- 27. Ph.D. Dissertation Defense July 14th , 2014 ● 6 x 1-m telescopes ● Dense [u,v] coverage ● MIRC combiner in H band ● 8 spectral channels ● 2010 – photometric channels ● 2011 – 6 telescope combination ● ~0.4 mas maximum resolution ● 27 epochs from 2007 to 2011 S1 S2 E1 E2 W2 W1 “Outer Array”, S1-E1-W1-W2 “Inner Array”, S2-E2-W1-W2 CHARA/MIRC
- 28. Ph.D. Dissertation Defense July 14th , 2014 Periodic Photometric Observations P1 = 26.978 ± 0.032 days P2 = 54.25 ± 0.91 days P3 = 55.0 ± 1.1 days P4 = 54.8 ± 1.9 days Pavg = 54.5 ± 2.4 days 2007 2008 2009 2010
- 29. Ph.D. Dissertation Defense July 14th , 2014 Parametric Model SQUEEZE Reconstruction ● GA and AMOEBA minimization ● Free parameters: ● Stellar angular diameter ● Limb-darkening coefficient ● Starspot size, latitude, longitude, and flux ratio ● ● Baron et. al 2010 ● Monte-Carlo Markov Chain minimization ● Minimizes flux gradients Starspots Artifact Angular Resolution
- 30. Ph.D. Dissertation Defense July 14th , 2014 2007 & 2008 Observing Strategy Nov 17th , 2007 ● 1 Inner Array snapshot Aug 17th through 21st , 2008 & Sep 20th and Sep 27th ,2008 ● 1 to 3 Outer Array snapshots [u,v] Coverage ● 48 to 144 points Each Data Block ● 6 visibilities ● 4 closure phase & triple amplitudes
- 31. Ph.D. Dissertation Defense July 14th , 2014 Inconclusive results based on limited [u,v] coverage 2007 & 2008 Data Sets
- 32. Ph.D. Dissertation Defense July 14th , 2014 2009 & 2010 Observing Strategy Aug 24th & Aug 25th , 2009 ●Bracketed obs. with Outer Array during night's first half ●Bracketed obs. with Inner Array during night's second half ●Combine both sets of data ●Repeat on consecutive night ●Combine nights together Aug 2nd through Sep 10th , 2010 ● Same as 2009 except Sep 10th [u,v] Coverage ● 624 to 1128 points (336 on Sep 10th ) Each Data Block ● 11 visibilities ● 8 closure phase & triple amplitudes Strategy provides nearly 8x improvement in [u,v] coverage and 2 additional closure phases
- 33. Ph.D. Dissertation Defense July 14th , 2014 Indicates presence of starspots even at maximum brightness 2009 Data Set Parameter Model Recon φ1 4.1 ± 4.1 3.6 b1 -2.3 ± 1.9 -3.4 l1 -13.4 ± 5.3 -26.8 Tr1 0.931 ± 0.024 0.922 φ2 2.2 ± 2.2 2.0 b2 -0.8 ± 1.4 -2.3 l2 22.9 ± 2.0 21.1 Tr2 0.979 ± 0.010 0.924
- 34. Ph.D. Dissertation Defense July 14th , 2014 2010 Data Set
- 35. Ph.D. Dissertation Defense July 14th , 2014 2010 Light Curve ● Points extracted from model images ● Scaled to match level and amplitude of photometric light curve
- 36. Ph.D. Dissertation Defense July 14th , 2014 2011 Observing Strategy Sep 2nd & Sep 24th , 2011 ●Bracketed obs. with all 6 telescopes simultaneously [u,v] Coverage ● 200 to 864 points Each Data Block ● 11 visibilities ● 20 closure phase & triple amplitudes Reduction in [u,v] coverage, however gains 12 additional closure phases
- 37. Ph.D. Dissertation Defense July 14th , 2014 2011 Data Set
- 38. Ph.D. Dissertation Defense July 14th , 2014 2011 Light Curve
- 39. Ph.D. Dissertation Defense July 14th , 2014 2010 λ Andromeda Rotation Pspots = 60 ± 13 days Pphot = 54.8 ± 1.9 days
- 40. Ph.D. Dissertation Defense July 14th , 2014 2011 λ Andromeda Rotation Pspots = 54.0 ± 7.6 days Pphot = 54.5 ± 2.4 days
- 41. Ph.D. Dissertation Defense July 14th , 2014 Still Don't Believe Me?
- 42. Ph.D. Dissertation Defense July 14th , 2014 Andromeda Rotation Axisλ 2010 2011 Φ = 20 ± 6.8° i = 78 ± 1.5° Φ = 23 ± 6.4° i = 77.98 ± 0.18°
- 43. Ph.D. Dissertation Defense July 14th , 2014 Conducted a high cadence, long baseline variability of the molecular cloud ρ Oph Characterized the amplitude and timescales of variability Discovered candidate ρ Oph members Discovered a number of stars with obvious evidence of multiple variability mechanisms Summary of Results I
- 44. Ph.D. Dissertation Defense July 14th , 2014 ● Established that cool spots can be resolved on stars besides the Sun. ● Tentative evidence for motion of cool starspots across stellar disc. ● Performed ~2.5 year variability survey with a cadence of ~1 day. ● Identified 101 variables from 1678 target stars ● Identified 32 periodic variable stars ● Determined variability time-scales for 31 stars ● Tentatively identified dominant variability mechanism for most variable stars Summary of Results II
- 45. Ph.D. Dissertation Defense July 14th , 2014 Acknowledgements
- 46. Ph.D. Dissertation Defense July 14th , 2014 Bonus Slides
- 47. Ph.D. Dissertation Defense July 14th , 2014 Plavchan-Parks Algorithm
- 48. Ph.D. Dissertation Defense July 14th , 2014 Determination of Time-scales
- 49. Ph.D. Dissertation Defense July 14th , 2014 Parameter Extraction from Reconstructions
- 50. Ph.D. Dissertation Defense July 14th , 2014 Simulated Images for Artifact Identification