Internal motions in OB-associations with Gaia DR2. (2020)
Keywords :
Galaxy open clusters and associations: general - kinematics and dynamics - stars: formation
Abstract:We study the motions inside 28 OB-associations with the use of Gaia DR2 proper motions. The average velocity dispersion calculated for 28 OB-associations including more than 20 stars with Gaia DR2 proper motion is sigma_v_=4.5km/s. The median virial and stellar masses of OB-associations are 8.9x10^5^ and 8.1x10^3^M_{sun}_, respectively. The median star-formation efficiency in parent giant molecular clouds appears to be epsilon=1.2%. Gaia DR2 proper motions confirm the expansion in the Per OB1, Car OB1 and Sgr OB1 associations found earlier with Gaia DR1 data. We also detect the expansion in Gem OB1, Ori OB1 and Sco OB1 associations which became possible for the first time now when analyzed with Gaia DR2 proper motions. The analysis of
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Table 1 lists the spectral, photometric and kinematic data for stars
in OB-associations. It presents the name of a star, the name of the
OB-association to which it is assigned by Blaha and Humphreys
(1989AJ.....98.1598B), spectral type of the star, code of its
luminosity class cL: 2 -- Ia, 4 -- Iab, 6 -- Ib, 8 -- II, 10 -- III,
12 -- IV, 14 -- V, where the corresponding odd numbers (1, 3,..., 13)
reflect the uncertainty in its determination. It also gives the
heliocentric distance to the OB-association by Blaha and Humphreys
(1989AJ.....98.1598B), r_BH_, reduced to the short distance
scale, r=0.8 r_BH_. Table 1 also lists Gaia DR2 data (2018, Cat.
I/345/gaia2) (2018A&A...616A...1G): the equatorial coordinates of the
star, its Galactic coordinates, the G-band magnitude, the parallax,
proper motions along the l- and b-directions and their errors. It also
presents the number of visibility periods, Nvis of the star, (Arenou
et al. 2018A&A...616A..17A), and the re-normalised unit weight error
(RUWE), which measures how well the Gaia observations agree with the
five-parameter single-star model and whose large value (RUWE>1.4)
could indicate an astrometric binary (Lindegren 2018, Gaia technical
note GAIA-C3-TN-LU-LL-124). We also added to Table 1 the stellar
line-of-sight velocities, Vr, and their errors, e_Vr, taken from the
catalog Barbier-Brossat and Figon (1999, Cat. III/213), which are
available for 52% of stars of OB-associations.
Anna Melnik, anna(at)sai.msu.ru
