2011A&A...525A.122P


Query : 2011A&A...525A.122P

2011A&A...525A.122P - Astronomy and Astrophysics, volume 525A, 122-122 (2011/1-1)

The evolution of luminosity, colour, and the mass-to-luminosity ratio of Galactic open clusters. Comparison of discrete vs. continuous IMF models.

PISKUNOV A.E., KHARCHENKO N.V., SCHILBACH E., ROESER S., SCHOLZ R.-D. and ZINNECKER H.

Abstract (from CDS):

We found in previous studies that standard simple stellar population (SSP) models are unable to describe or explain the colours of Galactic open clusters both in the visible and in the near-infrared (NIR) spectral range. The reason for this disagreement is the continuous nature of the stellar initial mass function (IMF) in clusters, which is the underlying assumption in the SSP models. In reality, the Galactic open clusters are sparsely populated with the brightest stars responsible for integrated fluxes. In this study, we aim at constructing discrete SSP-models that are able to adequately describe the observed magnitude-, colour-, and mass-to-luminosity-ratio-age relations of open clusters by including a number of seldom considered effects. We construct a numerical SSP-model with an underlying Salpeter IMF, which is valid within an upper mu and lower ml stellar mass range, and with the total masses Mc=102 ... 104m typical of open clusters. We assume that the mass loss from a cluster is provided by mass loss from evolved stars and by the dynamical evaporation of low-mass members because of two-body relaxation. The data for the latter process were scaled to the models from high-resolution N-body calculations. We also investigate how a change of the ml-limit influences the magnitudes and colours of clusters of a given mass and derive a necessary condition for a luminosity and colour flash. The discreteness of the IMF leads to bursts in the magnitude and colour of model clusters at moments when red supergiants or giants appear and then die. The amplitude of the burst depends on the cluster mass and on the spectral range; it is strongly increased in the NIR compared to optical passbands. In the discrete case variations of the parameter ml are able to substantially change the magnitude-age and M/L-age relations. For the colours, the lowering of ml considerably amplifies the discreteness effect. The influence of dynamical mass loss on colour and magnitude is weak, although it provides a change of the slopes of the considered relations, improving their agreement with observations. For the Galactic open clusters we determined luminosity and tidal mass independent of each other. The derived mass-to-luminosity ratio shows, on average, an increase with cluster age in the optical, but gradually declines with age in the NIR. The observed flash statistics can be used to constrain ml in open clusters.

Abstract Copyright:

Journal keyword(s): Galaxy: stellar content - galaxies: fundamental parameters - galaxies: starburst - galaxies: star clusters: general - galaxies: photometry - open clusters and associations: general

Simbad objects: 18

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Number of rows : 18
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 Cl Blanco 1 OpC 00 03 25 -29 57.5           ~ 279 0
2 Cl Stock 2 OpC 02 15 25 +59 31.3           ~ 106 0
3 NGC 869 OpC 02 18 58 +57 08.0           ~ 456 0
4 NGC 884 OpC 02 22 20 +57 08.9           ~ 467 0
5 Cl Melotte 20 OpC 03 26 28 +48 58.5           ~ 798 0
6 Cl Melotte 22 OpC 03 46 24 +24 06.8           ~ 3208 0
7 Cl Collinder 65 OpC 05 26 06 +16 42.0           ~ 30 0
8 NAME HIP 29713 Cluster MGr 06 15 26 +03 50.7           ~ 27 0
9 Ass Vel OB 2 As* 08 09 22.478 -47 21 03.46           ~ 245 0
10 NGC 2632 OpC 08 40 13 +19 37.3           ~ 1402 0
11 NAME HIP 45189 Cluster OpC 09 16 58 -43 51.7           ~ 40 0
12 Cl Turner 5 OpC 09 33 08 -36 21.5           ~ 30 0
13 Ass Nor OB 5 OpC 16 10 31 -49 00.8           ~ 19 0
14 Ass Sco OB 4 As* 17 12.6 -33 22           ~ 43 0
15 Ass Sco OB 5 As* 17 52.6 -38 38           ~ 13 0
16 Ass Sgr OB 7 As* 18 14.9 -20 24           ~ 39 0
17 Ass Cyg OB 2 As* 20 33.2 +41 19           ~ 878 0
18 NAME III CEP ASSOC As* 23 04.2 +63 24           ~ 310 0

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2022.08.10-07:19:32

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