J/A+A/595/A22 Nine new open clusters within 500pc from the Sun (Roser+, 2016)
Nine new open clusters within 500 pc from the Sun.
Roser S., Schilbach E., Goldman B.
<Astron. Astrophys., 595, A22 (2016)>
=2016A&A...595A..22R 2016A&A...595A..22R (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Proper motions ; Photometry
Keywords: catalogs - surveys - proper motions
Abstract:
One of the results of the Milky Way Star Clusters (MWSC) survey was
the detection of a slight under-density of old (ca. 1Gyr) clusters
within the nearest kilo-parsec from the Sun. This under-density may be
due to an ineffectiveness in the detection of larger structures with
lower surface brightness. We report on our attempts to reveal such
clusters.
We derived proper motions from a combination of Tycho-2 with URAT1,
and obtained a mean precision of about 1.4mas/yr per co-ordinate for
1.3 million stars north of -20° declination. We cut the sky into
narrow proper motion slices and searched for spatial over-densities of
stars in each slice. We then examined stars from over-densities in
optical and near-infrared colour-magnitude diagrams to determine if
they are compatible with isochrones of a cluster. We estimated the
field star contamination using our data and the Besancon Galactic
model.
We detected nine hitherto unknown open clusters in the vicinity of the
Sun with ages between 70Myr and 1Gyr, and distances between 200 and
500pc.
Description:
We used URAT1 (Zacharias et al., 2015, Cat. I/329) to improve the
Tycho-2 proper motions and to test what proper motions, which are more
precise than those of Tycho-2 (Hog et al., 2000, Cat. I/259), can do
for open cluster studies. URAT1 contains 228 million objects down to
about R=18.5 mag, north of about -20° declination. For the bulk of
the Tycho-2 stars, URAT1 gives positions at a mean epoch around 2013.5
and an accuracy level of about 20mas per co-ordinate. We cross-matched
URAT1 with Tycho-2 (the original data set tyc2.dat from CDS), and
obtained new proper motions via a least-squares adjustment as
described, for example in PPMXL (Roeser et al., 2010, Cat. I/317). To
avoid formally ultra-precise astrometry for a small number of stars,
we chose a 10mas floor for the precision of a URAT1 position.
The newly detected clusterings are located in the solar neighbourhood
at distances below 500pc from the Sun.
The candidates RSG1 to RSG8 are very probably genuine physical groups.
Membership and astrophysical parameters could be determined
sufficiently well. Nevertheless, accurate parallaxes of at least
several reliable cluster stars could improve the quality of parameter
determination. A definite age cannot be derived for RSG9; this
critically depends on the secure membership status of the two
brightest stars.
Table 1 summarises the astrophysical parameters of the newly found
objects.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 83 10 New open clusters
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Name Cluster name (RSGN, RSG9y RSG9o)
7- 8 I2 --- Nmenb Number of probable members
10- 15 F6.2 deg GLON Galactic longitude
17- 21 F5.2 deg GLAT Galactic latitude
23- 28 F6.2 deg RAdeg Cluster center right ascension (J2000.0)
30- 34 F5.2 deg DEdeg Cluster center declination (J2000.0)
36- 40 F5.2 mas/yr pmRA Average proper motion in RA*cos(DE)
42- 45 F4.2 mas/yr e_pmRA Standard error in pmRA
47- 52 F6.2 mas/yr pmDE Average proper motion in DE
54- 57 F4.2 mas/yr e_pmDE Standard error in pmDE
59- 61 I3 pc Dist Distance
63- 66 F4.2 [yr] logt Logarithm of age
68- 72 F5.1 pc Z Distance from the Galactic Plane
74- 78 F5.3 mag E(B-V) Colour-excess
80- 83 F4.2 mag MOD Apparent distance modulus
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Acknowledgements:
Siegfried Roeser, roeser(at)ari.uni-heidelberg.de
(End) Patricia Vannier [CDS] 02-Mar-2017