2009A&A...499..129L


Query : 2009A&A...499..129L

2009A&A...499..129L - Astronomy and Astrophysics, volume 499, 129-135 (2009/5-3)

Quantifying the contamination by old main-sequence stars in young moving groups: the case of the Local association.

LOPEZ-SANTIAGO J., MICELA G. and MONTES D.

Abstract (from CDS):

The associations and moving groups of young stars are excellent laboratories for investigating stellar formation in the solar neighborhood. Previous results have confirmed that a non-negligible fraction of old main-sequence stars is present in the lists of possible members of young stellar kinematic groups. A detailed study of the properties of these samples is needed to separate the young stars from old main-sequence stars with similar space motion, and identify the origin of these structures. Our intention is to characterize members of the young moving groups, determine their age distribution, and quantify the contamination by old main-sequence stars, in particular, for the Local Association. We used stars possible members of the young (∼10-650Myr) moving groups from the literature. To determine the age of the stars, we used several suitable age indicators for young main sequence stars, i.e., X-ray fluxes from the Rosat All-sky Survey database, photometric data from the Tycho-2, Hipparcos, and 2MASS database. We also used spectroscopic data, in particular the equivalent width of the lithium line LiI λ6707.8Å and Hα, to constrain the range of ages of the stars. By combining photometric and spectroscopic data, we were able to separate the young stars (10-650Myr) from the old (>1Gyr) field ones. We found, in particular, that the Local Association is contaminated by old field stars at the level of ∼30%. This value must be considered as the contamination for our particular sample, and not of the entire Local Association. For other young moving groups, it is more difficult to estimate the fraction of old stars among possible members. However, the level of X-ray emission can, at least, help to separate two age populations: stars with <200Myr and stars older than this. Among the candidate members of the classical moving groups, there is a non-negligible fraction of old field stars that should be taken into account when studying the stellar birthrate in the solar neighborhood. Our results are consistent with a scenario in which the moving groups contain both groups of young stars formed in a recent star-formation episode and old field stars with similar space motion. Only by combining X-ray and optical spectroscopic data is it possible to distinguish between these two age populations.

Abstract Copyright:

Journal keyword(s): Galaxy: stellar content - Galaxy: solar neighborhood - stars: kinematics - stars: activity - stars: coronae

Simbad objects: 35

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Number of rows : 35
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 NAME THA As* 00 00 -62.0           ~ 438 0
2 NGC 1039 OpC 02 42 07 +42 43.3           ~ 406 0
3 Cl Melotte 20 OpC 03 26 28 +48 58.5           ~ 819 0
4 Cl Melotte 22 OpC 03 46 24 +24 06.8           ~ 3279 0
5 Cl Melotte 25 OpC 04 29 47 +16 56.9           ~ 2928 0
6 NAME Tau-Aur Complex SFR 04 30 +25.0           ~ 1317 0
7 NAME Taurus Complex SFR 04 41.0 +25 52           ~ 4094 0
8 NAME Columba Association As* 06 04 19.4 -22 20 40           ~ 264 0
9 NAME AB Dor Moving Group MGr 06 38 53.4 -42 50 04           ~ 442 0
10 NGC 2516 OpC 07 58 06 -60 48.0           ~ 670 0
11 NGC 2632 OpC 08 40 13 +19 37.3           ~ 1449 0
12 IC 2391 OpC 08 41 10 -52 59.5           ~ 795 0
13 NAME eta Cha Association OpC 08 42 33 -78 57.8           ~ 351 0
14 IC 2602 OpC 10 42 27 -64 25.6           ~ 640 0
15 NAME UMa Region reg 11 00 +50.0           ~ 323 0
16 V* TW Hya TT* 11 01 51.9053285064 -34 42 17.033218380   11.94 10.50 10.626 9.18 K6Ve 1787 1
17 NAME TW Hya Association As* 11 01.9 -34 42           ~ 907 0
18 NAME eps Cha Association OpC 11 59 51 -78 12.4           ~ 147 1
19 Cl Melotte 111 OpC 12 24 03 +25 39.1           ~ 454 0
20 NAME Ursa Major Moving Group MGr 12 32 +57.0           ~ 420 2
21 NAME beta Pic Moving Group MGr 14 30 -42.0           ~ 710 0
22 HD 142764 * 15 56 44.5662772920 -10 03 42.483171276   11.39 9.56     K4/5 11 0
23 NAME Upper Sco-Cen As* 16 15 -24.2           ~ 1267 1
24 NAME Sco-Cen-Lup reg 16 20.0 -27 00           ~ 15 0
25 NAME Ophiuchus Molecular Cloud SFR 16 28 06 -24 32.5           ~ 3446 1
26 NAME NEP reg 18 00 00.000 +66 33 38.55           ~ 318 0
27 BD-10 4662 TT* 18 20 22.74972 -10 11 13.6263   12.00 10.62 10.24 8.884 K5Ve+K7Ve 83 0
28 NAME del Lyr Cluster OpC 18 54 16 +36 53.9   4.58 3.8     ~ 67 0
29 NAME CrA Complex reg 19 15 00.0 -37 30 00           ~ 106 1
30 V* AT Mic Er* 20 41 51.15925 -32 26 06.8283 12.753 11.909 10.343 9.098 7.383 M4.5Ve+M4.5Ve 350 0
31 NAME Octans Association As* ~ ~           ~ 83 0
32 NAME Castor Moving Group As* ~ ~           ~ 125 1
33 NAME Carina Moving Group MGr ~ ~           ~ 42 0
34 NAME Argus Association As* ~ ~           ~ 212 0
35 NAME Pleiades Moving Group MGr ~ ~           ~ 271 1

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2023.01.31-08:27:31

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