Early‐Type Stars in the Galactic Halo from the Palomar‐Green Survey. I. A Sample of Evolved, Low‐Mass Stars

1997 ◽  
Vol 111 (2) ◽  
pp. 419-444 ◽  
Author(s):  
N. C. Hambly ◽  
W. R. J. Rolleston ◽  
F. P. Keenan ◽  
P. L. Dufton ◽  
R. A. Saffer
Keyword(s):  
Galactic Halo ◽  
Early Type ◽  
Low Mass Stars ◽  
Low Mass ◽  
Early Type Stars

scholarly journals Giant planets around AF and M stars

2013 ◽  
Vol 8 (S299) ◽  
pp. 64-65
Author(s):  
Julien Rameau ◽  
Gaël Chauvin ◽  
Anne-Marie Lagrange ◽  
Philippe Delorme ◽  
Justine Lannier
Keyword(s):  
Giant Planets ◽  
Early Type ◽  
Late Type ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Planetary Mass ◽  
Nearby Stars ◽  
Low Mass ◽  
M Stars ◽  
The One

AbstractWe present the results of two three-year surveys of young and nearby stars to search for wide orbit giant planets. On the one hand, we focus on early-type and massive, namely β Pictoris analogs. On the other hand, we observe late type and very low mass stars, i.e., M dwarfs. We report individual detections of new planetary mass objects. According to our deep detection performances, we derive the observed frequency of giant planets between these two classes of parent stars. We find frequency between 6 to 12% but we are not able to assess a/no correlation with the host-mass.

scholarly journals Abundance Ratios in Metal-Poor Globular Clusters: Deep Mixing and its Effect on Stellar Populations of the Galactic Halo

1998 ◽  
Vol 11 (1) ◽  
pp. 53-57
Author(s):  
Robert P. Kraft
Keyword(s):  
Globular Clusters ◽  
Galactic Halo ◽  
Light Element ◽  
Asymptotic Giant Branch ◽  
Proton Capture ◽  
Low Mass Stars ◽  
Element Abundances ◽  
Deep Mixing ◽  
Low Mass ◽  
Red Giant

Only a bit more than 25 years ago, it seemed possible to assume that all Galactic globular clusters were chemically homogeneous. There were indications that star-to-star Fe abundance variations existed in ω Cen, but this massive cluster appeared to be unique. Following Osborn’s (1971) initial discovery, Zinn’s (1973) observation that M92 asymptotic giant branch (AGB) stars had weaker G-bands than subgiants with equivalent temperatures provided the first extensive evidence that there might be variations in the abundances of the light elements in an otherwise “normal” cluster. Since then star-to-star variations in the abundances of C, N, O, Na, Mg and Al have been observed in all cases in which sample sizes have exceeded 5-10 stars, e.g., in clusters such as M92, M15, M13, M3, ω Cen, MIO and M5. Among giants in these clusters one finds large surface O abundance differences, and these are intimately related to differences of other light element abundances, not only of C and N, but also of Na, Mg and Al (cf. reviews by Suntzeff 1993, Briley et al 1994, and Kraft 1994). The abundances of Na and O, as well as Al and Mg, are anticorrelated. Prime examples are found among giants in M15 (Sneden et al 1997), M13 (Pilachowski et al 1996; Shetrone 1996a,b; and Kraft et al 1997) and ω Cen (Norris & Da Costa 1995a,b). These observed anticorrelations almost certainly result from proton- capture chains that convert C to N, 0 to N, Ne to Na and Mg to Al in or near the hydrogen fusion layers of evolved cluster stars. But which stars? An appealing idea is that during the giant branch lifetimes of the low-mass stars that we now observe, substantial portions of the stellar envelopes have been cycled through regions near the H-burning shell where proton-capture nucleosynthesis can occur. This so-called “evolutionary” scenario involving deep envelope mixing in first ascent red giant branch (RGB) stars has been studied by Denissenkov & Denissenkova (1990), Langer & Hoffman (1995), Cavallo et al (1996, 1997) and Langer et al (1997). The mixing mechanism that brings proton-capture products to the surface is poorly understood (Denissenkov & Weiss 1996, Denissenkov et al 1997, Langer et al 1997), but deep mixing driven by angular momentum has been suggested (Sweigart & Mengel 1979, Kraft 1994, Langer & Hoffman 1995, Sweigart 1997).

scholarly journals Variation in the Stellar Initial Mass Function from the Chromospheric Activity of M Dwarfs in Early-type Galaxies

2021 ◽  
Vol 923 (1) ◽  
pp. 43
Author(s):  
Pieter van Dokkum ◽  
Charlie Conroy
Keyword(s):  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Early Type ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Chromospheric Activity ◽  
Stellar Initial Mass Function ◽  
Low Mass ◽  
The Imf

Abstract Mass measurements and absorption-line studies indicate that the stellar initial mass function (IMF) is bottom-heavy in the central regions of many early-type galaxies, with an excess of low-mass stars compared to the IMF of the Milky Way. Here we test this hypothesis using a method that is independent of previous techniques. Low-mass stars have strong chromospheric activity characterized by nonthermal emission at short wavelengths. Approximately half of the UV flux of M dwarfs is contained in the λ1215.7 Lyα line, and we show that the total Lyα emission of an early-type galaxy is a sensitive probe of the IMF with a factor of ∼2 flux variation in response to plausible variations in the number of low-mass stars. We use the Cosmic Origins Spectrograph on the Hubble Space Telescope to measure the Lyα line in the centers of the massive early-type galaxies NGC 1407 and NGC 2695. We detect Lyα emission in both galaxies and demonstrate that it originates in stars. We find that the Lyα to i-band flux ratio is a factor of 2.0 ± 0.4 higher in NGC 1407 than in NGC 2695, in agreement with the difference in their IMFs as previously determined from gravity-sensitive optical absorption lines. Although a larger sample of galaxies is required for definitive answers, these initial results support the hypothesis that the IMF is not universal but varies with environment.

scholarly journals IMF radial gradients in most massive early-type galaxies

2019 ◽  
Vol 489 (3) ◽  
pp. 4090-4110 ◽  
Author(s):  
F La Barbera ◽  
A Vazdekis ◽  
I Ferreras ◽  
A Pasquali ◽  
C Allende Prieto ◽  
...  
Keyword(s):  
Stellar Population ◽  
Velocity Dispersion ◽  
Mass Density ◽  
Initial Mass Function ◽  
Early Type ◽  
Low Mass Stars ◽  
Surface Mass ◽  
Low Mass ◽  
Surface Mass Density ◽  
The Imf

ABSTRACT Using new long-slit spectroscopy obtained with X-Shooter at ESO-VLT, we study, for the first time, radial gradients of optical and near-infrared initial mass function (IMF)-sensitive features in a representative sample of galaxies at the very high mass end of the galaxy population. The sample consists of seven early-type galaxies (ETGs) at z ∼ 0.05, with central velocity dispersion in the range 300 ≲ σ ≲ 350 km s−1. Using state-of-the-art stellar population synthesis models, we fit a number of spectral indices, from different chemical species (including TiO and Na indices), to constrain the IMF slope (i.e. the fraction of low-mass stars), as a function of galactocentric distance, over a radial range out to ∼4 kpc. ETGs in our sample show a significant correlation of IMF slope and surface mass density. The bottom-heavy population (i.e. an excess of low-mass stars in the IMF) is confined to central galaxy regions with surface mass density above $\rm \sim 10^{10}\, M_\odot \, kpc^{-2}$, or, alternatively, within a characteristic radius of ∼2 kpc. Radial distance, in physical units, and surface mass density are the best correlators to IMF variations, with respect to other dynamical (e.g. velocity dispersion) and stellar population (e.g. metallicity) properties. Our results for the most massive galaxies suggest that there is no single parameter that fully explains variations in the stellar IMF, but IMF radial profiles at z ∼ 0 rather result from the complex formation and mass accretion history of galaxy inner and outer regions.

An upper limit on the density of low-mass stars in the Galactic halo

Nature ◽  
1994 ◽  
Vol 371 (6497) ◽  
pp. 493-495 ◽  
Author(s):  
E. M. Hu ◽  
J.-S. Huang ◽  
G. Gilmore ◽  
L. L. Cowie
Keyword(s):  
Galactic Halo ◽  
Low Mass Stars ◽  
Upper Limit ◽  
Low Mass

scholarly journals X-ray properties of early-type stars

1994 ◽  
Vol 162 ◽  
pp. 200-201
Author(s):  
Thomas W. Berghöfer ◽  
Jürgen H. M. M. Schmitt
Keyword(s):  
Survey Data ◽  
Early Type ◽  
Late Type ◽  
X Ray ◽  
Sky Survey ◽  
Low Mass ◽  
Early Type Stars ◽  
Einstein Observatory ◽  
Hr Diagram

Extensive stellar surveys with the Einstein Observatory (Chlebowski et al., 1989) and with ROSAT have clearly confirmed the presence of stellar X-ray emission over nearly the whole range of the HR diagram. In the ROSAT all-sky survey data approximately 20000 stellar X-ray sources were detected (Schmitt et al., 1992). Most of these stellar X-ray emitters are low mass late-type stars, the origin of their X-ray emission is thought to be coronal.

scholarly journals Did globular clusters contribute to the stellar population of the Galactic halo?

2015 ◽  
Vol 11 (S317) ◽  
pp. 104-109
Author(s):  
Corinne Charbonnel ◽  
Martin Krause
Keyword(s):  
Globular Clusters ◽  
Massive Star ◽  
Stellar Population ◽  
Local Group ◽  
Galactic Halo ◽  
Chemical Properties ◽  
Star Clusters ◽  
Alternative Interpretation ◽  
Low Mass Stars ◽  
Low Mass

AbstractThe origin of Galactic halo stars and the contribution of globular clusters (GC) to this stellar population have long been (and still are) debated. The discovery of multiple stellar populations with peculiar chemical properties in GCs both in the Milky Way and in Local Group galaxies recently brought a renewal on these questions. Indeed most of the scenarios that compete to reproduce the present-day GC characteristics call for fast expulsion of both gas and low-mass stars from these clusters in their early infancy. In this framework, the initial masses of GCs could have been 8 to 25 times higher than their present-day stellar mass, and they could have contributed to 5 to 20 % of the low-mass stars in the Galactic halo. Here we revisit these conclusions, which are in tension with observations of dwarf galaxies and of young massive star clusters in the Local Group. We come back in particular on the paradigm of gas expulsion from massive star clusters, and propose an alternative interpretation of the GC abundance properties. We conclude by proposing a major revision of the current concepts regarding the role massive star clusters play in the assembly of galactic haloes.

scholarly journals The XLENS Project: Do More Massive Early-Type Galaxies Have More Dark Matter or Different Stellar IMFs?

2012 ◽  
Vol 8 (S295) ◽  
pp. 221-224
Author(s):  
Chiara Spiniello
Keyword(s):  
Dark Matter ◽  
Gravitational Lensing ◽  
Population Analysis ◽  
Mass Function ◽  
Initial Mass Function ◽  
Early Type ◽  
Stellar Content ◽  
Low Mass Stars ◽  
Very Large Telescope ◽  
Low Mass

AbstractThe X-shooter Lens Survey (XLENS) aims to study the interplay of dark matter (DM) and stellar content in the inner regions of massive early-type galaxies (ETGs) by combining strong gravitational lensing, dynamical models, and spectroscopic stellar population analysis. XLENS targets a sample of ETGs from the SLACS survey (The Sloan Lens ACS Survey, e.g. Bolton et al. 2006) with velocity dispersions ≥250 kms−1 using the X-Shooter spectrograph on ESO's Very Large Telescope. Recent observations indicate that the internal dark-matter fraction of ETGs increases rapidly with galaxy mass, although some hints for a varying initial mass function (IMF) have also been suggested, where the low-mass end of the stellar IMF steepens with galaxy mass. XLENS first results unambiguously confirm that DM plays an important role already within one effective radius for very massive systems (Spiniello et al. 2011). Moreover, studying equivalent widths of certain red spectral features which are indicators of low-mass stars in massive ETGs (e.g. NaI and TiO2) as a function of age and metallicity (i.e. Mgb, Fe, Hβ), and as function of stellar velocity dispersion, has shown that the IMF slope is varying mildly with galaxy mass (Spiniello et al. 2012).

scholarly journals Early-type stars in the Galactic halo from the Palomar-Green survey - III. Completion of a magnitude range limited sample

2004 ◽  
Vol 349 (3) ◽  
pp. 821-832 ◽  
Author(s):  
B. B. Lynn ◽  
F. P. Keenan ◽  
P. L. Dufton ◽  
R. A. Saffer ◽  
W. R. J. Rolleston ◽  
...  
Keyword(s):  
Galactic Halo ◽  
Early Type ◽  
Limited Sample ◽  
Magnitude Range ◽  
Early Type Stars
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