We investigate the distance and three-dimensional spacial distribution of the young stellar cluster IC348 using newly available, highly precise par- allax and position data from the Gaia astrometry mission’s Data Release 2

1. A Study of the Young Stellar Cluster IC348 with
Gaia Data Release 2
Madeline Boyce
Center for Imaging Science
Rochester Institute of Technology
August 3, 2018
Abstract
We investigate the distance and three-dimensional spacial distribution
of the young stellar cluster IC348 using newly available, highly precise par-
allax and position data from the Gaia astrometry mission’s Data Release
2 (DR2). We found all 478 confirmed IC348 members listed in Luhman
et al 2016 have entries in the DR2 catalog that appear to correspond in
position. We limited the sample studied here to 173 targets by excluding
those stars whose parallax error was larger than 25 parsecs, and whose
coordinates in Luhman et al. 2016 and Gaia DR2 differed by greater than
1”. We find the mean distance to the cluster to be 311 ± 32 parsecs. An
interactive 3D map of IC348 was created using Plotly in Python. Rela-
tions between spectral type and class type and location in the cluster were
also studied. M and K type stars appeared to lie somewhat closer than
the mean cluster distance, however it is likely this is simply a result of
sampling, as M and K type stars are fainter and therefore more difficult
to detect at greater distances. We also compare the distributions of class
II and class III stars (the sample did not contain any class I stars). Ra-
dial velocities were also studied to determine if IC348 was expanding or
contracting.
1 Introduction
The goal of this paper is to calculate precise distances to and space velocities
of members of the star forming cluster IC348 using new Gaia data. IC348
is estimated to be 2-3 million years old and lies in the Perseus constellation.
Space velocities can tell us about the formation and dispersion of the cluster.
The distance can tell us about the age and luminosity of the stars. A shorter
distance means a lower luminosity and older age, while a longer distance means
a brighter luminosity and younger age. Properly knowing the space velocities
and distances of these stars can help us learn about the formation and dispersion
of the star cluster, which in turn can help us learn more about our own solar
neighborhood in the days of its youth.
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2. 2 Methods
This research utilizes information found in the Gaia Data Release 2 (DR2)
archives. Gaia is a space observatory run by the European Space Agency (ESA),
whose mission is to measure extremely precise parallax angles of a billion stars,
as well as proper motion, radial velocity, and other measurements not studied
in this paper. The precision and sheer amount of data taken and released by
Gaia is changing the astronomy world. This paper focuses on the parallax and
distance aspects of Gaia.
We started with 478 potential members of IC348 from Luhman et al. 2016.
Most the stars listed in that paper were listed with 2MASS identifier names,
which turned out to be a problem. The Gaia archive failed to resolve 2MASS
identifiers from an input file. The issue appeared to stem from the ’+’ character
used in 2MASS names for stars in the northern hemisphere, where IC348 is
located. This bug was reported and has since been fixed, although we had to
use different identifiers and coordinates to pull data from the archive. Once we
found the 478 potential members in the archive, we converted the parallax angle
into a distance measurement.
distance =
1
parallax
(1)
The error in the distance was then calculated. However, simply calculating the
inverse of the parallax angle error would not work to find the distance. Since
the angle error is so small, the distance error would appear to be larger than
that distance itself. The equation to calculate distance error is:
distanceerror = ±
1
parallax + parallaxerror
−
1
parallax
(2)
The targets with error larger than 25 parsecs were then trimmed away, as well
as those whose Gaia coordinates differed from the input coordinates by greater
than 1”, which left 173 targets. The targets were then categorized by their stellar
class type: class I, class II, or class III. The sample contained no class I objects.
A histogram of the distances was made for each class type and compared to
the sample as a whole (figure 1 a,b,c). Each target was also plotted in the 3-
dimensional map and color coded by class type (figure 2 a), so as to study the
relation between class type and location in the cluster.
3 Results and Conclusions
The mean distance to the cluster was found by fitting a gaussian to the distance
histogram of all the targets and was found to be 311 ± 32 parsecs. The mean
distance to class II objects was found to be 305 ± 32 parsecs, while the mean
distance to class III objects was found to be 315 ± 31 parsecs. The distances
appear to differ slightly based on class type, however the differences lie within
the error of the cluster as a whole. Class II objects tend to be fainter than class
2

3. III objects, and are therefore more difficult to detect and measure at further
distances. Looking at the cartesian position map of IC348, there does not seem
to be any obvious grouping or inhomogeneous distribution of the two class types.
The apparent difference in the distances of class types is therefore likely an issue
of sampling.
The proper motion in the right ascension and declination and the radial
velocity[1]
were converted into UVW coordinates using the Kinematics Calcu-
lator from BDNYC[7]
and plotted in a 3-dimensional map (figure 2 b). Most
of the stars are grouped together in this plot, showing that their velocities are
very similar. This suggests that the targets are moving together and are indeed
part of the cluster. These UVW coordinates can be used to determine if IC348
is bound or expanding (or has ”puzzling signs of convergence” as Cottaar et
al. 2015 claims), however this particular point has not been studied enough in
this paper to give any sort of answer. A further analysis of the velocities, and
perhaps digging into the redshifts of the targets, is needed.
How do these new calculations compare to old estimates? In some instances,
Gaia has completely changed everything that we thought we knew about the
objects in question. This, however, is not th11.e case with IC348. Previous
papers have used an adopted distance of 310 ± 20 parsecs[8]
, which is only 1
parsec away from the distance of 311 ± 32 parsecs found in this paper, and
clearly lies within the error. This means that the estimated age of 2-3 million
years old is still accurate, as is the estimated luminosity distribution.
4 References
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3

4. (a) Histogram of distance to the members
of IC348 fit with a Gaussian.
(b) Histogram of distance of class II mem-
bers superimposed on histogram of all
members and fit with Gaussian.
(c) Histogram of distance of class III mem-
bers superimposed on histogram of all
members and fit with Gaussian.
Figure 1: Distance Histograms of IC348
4

5. (a) a 3 dimensional map of IC348. Blue points are
class II objects and red points are class III objects.
(b) a 3 dimensional map of the velocity of IC348 in
UVW coordinates, calculated from proper motion
and radial velocity.
Figure 2: Maps of IC348
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6. Field Near-Infrared Images. The Astronomical Journal,125(4), 2029-2049. doi:
10.1086/373925
[7] Rodriguez, D. (2018). BDNYC Kinematics Calculator. [online] Kinemat-
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Caceres, C., Canovas, H., Casassus, S., Schreiber, M. and Kastner, J. (2018).
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