2002ApJ...569..975R


C.D.S. - SIMBAD4 rel 1.7 - 2020.11.30CET22:54:05

2002ApJ...569..975R - Astrophys. J., 569, 975-983 (2002/April-3)

On the observational properties of he-burning stars: some clues on the tilt of the horizontal branch in metal-rich clusters.

RAIMONDO G., CASTELLANI V., CASSISI S., BROCATO E. and PIOTTO G.

Abstract (from CDS):

We investigate the predicted color-magnitude distribution of metal-rich horizontal-branch (HB) stars, discussing selected theoretical models computed under various assumptions about the star metallicity and the efficiency of superadiabatic convection. We find that canonical zero-age horizontal branches with metallicity larger or of the order of Z=0.002 should all be affected by a tilt by an amount that increases when the metallicity is increased and/or the mixing length is decreased, reaching a tilt of ΔV∼0.2 mag in the case of solar metallicity when a mixing-length value α=1.6 is assumed (ΔV is the magnitude difference between the top of the blue HB and the fainter magnitude reached by the red HB). Uncertainties in the luminosity of the red HB due to uncertainty in the mixing-length value are discussed. We finally discuss the much larger tilt observed in the clusters NGC 6441 and NGC 6388, reporting additional evidence against suggested noncanonical evolutionary scenarios. Numerical experiments show that differential reddening could produce such sloped HBs. Furthermore, Hubble Space Telescope planetary-camera imaging of NGC 6441 gives clear indications of the occurrence of differential reddening across the cluster. However, the same imaging shows that the observed slope of the red HB is not an artifact of differential reddening. We finally show that sloping red HBs in metal-rich clusters are a common occurrence not necessarily correlated with the appearance of extended blue HBs.

Abstract Copyright:

Journal keyword(s): Galaxy: Globular Clusters: General - globular clusters: individual (NGC 6388, NGC 6441) - Stars: Evolution - Stars: Horizontal-Branch

Simbad objects: 13

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Number of rows : 13

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 NGC 104 GlC 00 24 05.359 -72 04 53.20   5.78 4.09     ~ 3584 0
2 NGC 1851 GlC 05 14 06.76 -40 02 47.6   8.80 7.23     ~ 1253 0
3 NGC 2808 GlC 09 12 03.10 -64 51 48.6   7.77 5.69     ~ 1258 0
4 NGC 5927 GlC 15 28 00.69 -50 40 22.9   10.13 8.86     ~ 407 0
5 NGC 6229 GlC 16 46 58.641 +47 31 36.38   9.38 9.86     ~ 315 0
6 NGC 6304 GlC 17 14 32.25 -29 27 43.3   10.33 9.03     ~ 302 0
7 NGC 6356 GlC 17 23 34.99 -17 48 46.9   10.01 7.42     ~ 321 1
8 NGC 6362 GlC 17 31 54.99 -67 02 54.0   9.72 8.86     ~ 494 0
9 NGC 6388 GlC 17 36 17.461 -44 44 08.34   7.40       ~ 813 1
10 NGC 6441 GlC 17 50 13.06 -37 03 05.2   9.26 8.00     ~ 775 0
11 NGC 6624 GlC 18 23 40.51 -30 21 39.7           ~ 782 1
12 NGC 6712 GlC 18 53 04.32 -08 42 21.5   9.85 8.69     ~ 472 0
13 M 30 GlC 21 40 22.12 -23 10 47.5     7.10     ~ 927 0

    Equat.    Gal    SGal    Ecl

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2020.11.30-22:54:05

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