2007ApJ...671..748K


C.D.S. - SIMBAD4 rel 1.7 - 2019.10.16CEST01:12:20

2007ApJ...671..748K - Astrophys. J., 671, 748-760 (2007/December-2)

Stellar evolution in NGC 6791: mass loss on the red giant branch and the formation of low-mass white dwarfs.

KALIRAI J.S., BERGERON P., HANSEN B.M.S., KELSON D.D., REITZEL D.B., RICH R.M. and RICHER H.B.

Abstract (from CDS):

We present the first detailed study of the properties (temperatures, gravities, and masses) of the NGC 6791 white dwarf population. This unique stellar system is both one of the oldest (8 Gyr) and most metal-rich ([Fe/H]~+0.4) open clusters in our Galaxy and has a color-magnitude diagram (CMD) that exhibits both a red giant clump and a much hotter extreme horizontal branch. Fitting the Balmer lines of the white dwarfs in the cluster using Keck/LRIS spectra suggests that most of these stars are undermassive, <M≥0.43±0.06 M, and therefore could not have formed from canonical stellar evolution involving the helium flash at the tip of the red giant branch. We show that at least 40% of NGC 6791's evolved stars must have lost enough mass on the red giant branch to avoid the flash and therefore did not convert helium into carbon-oxygen in their core. Such increased mass loss in the evolution of the progenitors of these stars is consistent with the presence of the extreme horizontal branch in the CMD. This unique stellar evolutionary channel also naturally explains the recent finding of a very young age (2.4 Gyr) for NGC 6791 from white dwarf cooling theory; helium-core white dwarfs in this cluster will cool ∼3 times slower than carbon-oxygen-core stars, and therefore the corrected white dwarf cooling age is in fact ≳7 Gyr, consistent with the well-measured main-sequence turnoff age. These results provide direct empirical evidence that mass loss is much more efficient in high-metallicity environments and therefore may be critical in interpreting the ultraviolet upturn in elliptical galaxies.

Abstract Copyright:

Journal keyword(s): Galaxy: Open Clusters and Associations: Individual: NGC Number: NGC 6791 - Stars: Evolution - Stars: Mass Loss - Techniques: Photometric - Techniques: Spectroscopic - Stars: White Dwarfs

Nomenclature: Table 2: Cl* NGC 6791 KBH NN (Nos 1-14).

Simbad objects: 29

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Number of rows : 29

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2019
#notes
1 M 32 IG 00 42 41.825 +40 51 54.61 9.51 9.03 8.08     ~ 1969 2
2 M 31 G 00 42 44.330 +41 16 07.50 4.86 4.36 3.44     ~ 10560 1
3 NGC 188 OpC 00 48 26 +85 15.3           ~ 792 0
4 Cl Melotte 25 OpC 04 26 54.00 +15 52 00.0           ~ 2579 0
5 Cl Berkeley 17 OpC 05 20 37 +30 35.4           ~ 129 0
6 M 37 OpC 05 52 18 +32 33.2   6.19 5.6     ~ 327 2
7 NGC 2168 OpC 06 08 54 +24 20.0           ~ 447 0
8 NGC 2323 OpC 07 02 47.5 -08 20 16           ~ 152 0
9 NGC 2682 OpC 08 51 18 +11 48.0           ~ 1981 0
10 HZ 21 WD* 12 13 56.2639830406 +32 56 31.359805342 13.125 14.361 14.688 14.837 15.038 DO1 134 0
11 M 4 GlC 16 23 35.22 -26 31 32.7           ~ 1630 0
12 NGC 6397 GlC 17 40 42.09 -53 40 27.6   7.39 5.17     ~ 1749 1
13 NGC 6752 GlC 19 10 52.11 -59 59 04.4   6.96 6.28     ~ 1763 0
14 Cl* NGC 6791 KBH 7 WD* 19 20 42.50 +37 44 12.9   23.88 23.54     DA 6 0
15 Cl* NGC 6791 KBH 10 WD* 19 20 47.00 +37 46 29.0   23.83 23.80     DA 2 0
16 Cl* NGC 6791 KBH 5 WD* 19 20 47.30 +37 44 37.3   22.97 22.82     DA 2 0
17 Cl* NGC 6791 KBH 6 WD* 19 20 48.20 +37 47 18.1   23.63 23.28     DA 2 0
18 Cl* NGC 6791 KBH 1 WD* 19 20 48.6136755903 +37 45 49.631122380   21.79 21.91     DA 2 1
19 NGC 6791 OpC 19 20 53 +37 46.3   10.52 9.5     ~ 840 0
20 Cl* NGC 6791 KBH 9 WD* 19 20 56.90 +37 44 15.2   23.93 23.60     DA 2 0
21 Cl* NGC 6791 KBH 4 WD* 19 20 58.40 +37 45 55.5   23.56 23.47     DA 2 0
22 Cl* NGC 6791 KBH 12 WD* 19 21 02.90 +37 47 27.0   24.21 23.97     DA 2 0
23 Cl* NGC 6791 KBH 2 WD* 19 21 04.10 +37 44 43.3   22.19 22.19     DA 2 0
24 Cl* NGC 6791 KBH 11 blu 19 21 05.80 +37 46 51.5   23.73 23.87     ~ 1 0
25 Cl* NGC 6791 KBH 14 blu 19 21 06.50 +37 44 10.5   24.28 24.04     ~ 1 0
26 Cl* NGC 6791 KBH 13 WD* 19 21 08.30 +37 44 30.2   24.34 24.02     DA 2 0
27 Cl* NGC 6791 KBH 3 WD* 19 21 10.50 +37 45 51.2   22.96 22.68     DA 2 0
28 Cl* NGC 6791 KBH 8 WD* 19 21 13.60 +37 43 20.0   23.81 23.59     DA 3 0
29 NGC 6819 OpC 19 41 18 +40 11.2   8.21 7.3     ~ 439 0

    Equat.    Gal    SGal    Ecl

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2019.10.16-01:12:20

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