Luminosity Function Of Stars Research Articles

Possible observational consequences of primordial binaries in globular clusters

The paper investigates the observational consequences of the evolution of a primordial binary population in a globular cluster. For those binary systems which begin mass transfer at orbital periods of less than about 1 d, the system is expected to evolve to a contact binary stage and to eventually merge to form a single star. At longer orbital periods, the binary system will enter into a common envelope stage. For periods less than about 10 d, the system is likely to merge, and the outcome of the evolution is a single red giant star. For systems characterized by orbital periods greater than about 15 d, a detached red dwarf-white dwarf binary system is expected to change. As a consequence of the mergers, a range in masses for the red giant stars is possible, leading to a color spread on the RGB of the color magnitude diagram. The luminosity function of stars at high luminosities is expected to steepen as a result of tidal interaction in the binary. It is suggested that the formation of cataclysmic variables via primordial binaries is expected only in loosely bound clusters of low-velocity dispersion.

The luminosity function of halo white dwarfs

Recently, Liebertet al. (1989) have obtained an approximate observational luminosity function for halo white dwarfs. Certainly, this first attempt will be improved by the forthcoming Very Large Telescopes. Here we construct theoretical luminosity functions of such stars and we examine their dependence on the age of the halo. Finally, we show that accurate observational luminosity functions could provide useful information about the evolution of the galaxy.

The asymptotic giant branch of Magellanic Cloud clusters

view Abstract Citations (268) References (77) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Asymptotic Giant Branch of Magellanic Cloud Clusters Frogel, Jay A. ; Mould, Jeremy ; Blanco, V. M. Abstract Thirty-nine clusters in the Magellanic Clouds have been surveyed for carbon and M-type asymptotic giant branch (AGB) stars. We identified and obtained near-infrared photometry for about 400 such stars in and around the clusters. The cluster classification scheme of Searle, Wilkinson, and Bagnuolo (SWB), which we show to be closely correlated with cluster age, is a key element in the analysis of our data. The principal results of our investigation are as follows. In a C-M diagram the cluster M stars shift steadily redward in J-K as one goes from clusters of SWB type I to VI. This is due to the increasing age of the clusters along the sequence. There are two peaks in the color distribution of the M stars which could indicate two epochs of enhanced cluster formation: one about 100 Myr ago, the other about 1 Gyr ago. These correspond to similar enhancements deduced for M stars in the Bar West region of the LMC. For LMC clusters in the 1 Gyr old group we estimate the spread in [Fe/H] to be on the order of 0.2-0.3 dex. This implies that chemical enrichment was fairly uniform throughout the LMC at that epoch. The brightest stars in SWB type VII clusters have luminosities and colors that are closely comparable to the brightest stars in Galactic globular clusters; with one possible exception they have no luminous AGB stars. We deduce that the SWB VII clusters in the Clouds are as old as Galactic globular clusters and have a range in metallicity of about a factor of 10. Luminous carbon stars are present only in SWB IV-VI clusters. They are easily distinguished from M stars by their color and luminosity. The effects of age and metallicity are apparent in luminosity functions for C stars: for those in SWB type VI clusters the luminosity function is several tenths of a magnitude fainter than that for earlier type clusters: both cluster and field SMC C stars are intrinsically fainter than their LMC counterparts. The shape of the luminosity functions for C stars from the various types of clusters are consistent with each being drawn from the same sample of field stars in the Clouds, so that the latter is clearly a composite population with a range in age and metallicity that must closely overlap that for the clusters. For the SWB-type clusters in which C stars are present, they are almost always brighter than the M stars in the same clusters. The transition luminosity between the two types of stars gets systematically brighter as one passes from the latest to the earliest type clusters. The existence of such a transition luminosity is an important prediction of the theory of carbon star formation and evolution. The youngest clusters in which C stars are found have an age of about 100 Myr implying a maximum initial mass for these stars of 3-5 M_sun_. In clusters younger than 100 Myr, the brightest stars are M giants; even though these are the brightest stars in the entire sample, they still cannot account for the missing luminous AGB stars. Therefore, the hypothesis that luminous C stars turn back into M stars appears to be ruled out. Convective overshooting or high mass-loss rates are promising hypotheses for the absence of luminous C stars. The former could also explain the fact that we see luminous C stars in clusters with turnoff masses as low as 1.0 M_sun_ in the SMC. In intermediate-age clusters, ~40% of the bolometric luminosity is contributed by C and M type AGB stars, a somewhat smaller fraction than predicted by Renzini and Buzzoni. However, because the C star luminosity function is shifted to fainter magnitudes than predicted, the age range in which AGB stars make a significant contribution is shifted to substantially older ages. If the contribution of AGB stars is removed from a cluster's light, the resulting distribution of integrated J-K colors shows a jump at types IV-V. This corresponds to the age at which the helium core switches from being degenerate to nondegenerate and is in reasonable agreement with theory. Publication: The Astrophysical Journal Pub Date: March 1990 DOI: 10.1086/168518 Bibcode: 1990ApJ...352...96F Keywords: Asymptotic Giant Branch Stars; Carbon Stars; Globular Clusters; M Stars; Magellanic Clouds; Color-Magnitude Diagram; Hertzsprung-Russell Diagram; Interstellar Extinction; Metallicity; Star Formation; Stellar Luminosity; Stellar Spectrophotometry; Astrophysics; CLUSTERS: GLOBULAR; GALAXIES: MAGELLANIC CLOUDS; STARS: CARBON; STARS: EVOLUTION; STARS: LATE-TYPE full text sources ADS | data products SIMBAD (301) NED (40)

A comparison of the luminosity functions in U, B, and V and their relationship to the initial mass function for the Galaxy and the Magellanic Clouds

view Abstract Citations (141) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Comparison of the Luminosity Functions in U, B, and V and Their Relationship to the Initial Mass Function for the Galaxy and the Magellanic Clouds Blaha, Cynthia ; Humphreys, Roberta M. Abstract From our compilation of luminous O and B stars and supergiants of all spectral types, we have calculated the U, B, and V luminosity functions for stars within 3 kpc in our galaxy and the Magellanic Clouds. The luminosity functions are quite similar at all wavelengths, and the slight differences observed reflect variations in the sample size and degree of completeness. In the range -9 <= M_v_ <= -7, we find that the U, B, and V luminosity functions in both our galaxy and the Clouds have a slope of roughly + 0.7. The present-day initial mass function has also been calculated for these samples of stars. Within the uncertainties, our results are consistent with ψ(M) [the number of stars per kpc per year per log (M/M_sun_)] proportional to (M)^-2^ for the 25-85 M_sun_ range. The slopes for the Magellanic Clouds may be slightly flatter than in our galaxy, but there is probably incompleteness at the lower mass intervals. The impact of a luminous young cluster on the luminosity and mass functions was studied through the addition of stars from the 30 Doradus region to our LMC sample. Although this addition nearly doubled our population of early O stars, the U, B, and V luminosity functions remained essentially unchanged. However, the slope of the initial mass function flattened with the addition of the 30 Doradus sample. This flattening may be artificially produced by the lack of faint late O and early B stars in the 30 Dor sample which have not yet been studied. Publication: The Astronomical Journal Pub Date: November 1989 DOI: 10.1086/115244 Bibcode: 1989AJ.....98.1598B Keywords: Galactic Mass; Luminosity; Magellanic Clouds; Milky Way Galaxy; Ubv Spectra; B Stars; Galactic Evolution; O Stars; Supergiant Stars; Astrophysics; STARS: LUMINOSITY FUNCTION; GALAXIES: THE GALAXY; GALAXIES: MAGELLANIC CLOUDS full text sources ADS | data products SIMBAD (4) NED (2)

The mass and luminosity of cool dwarf stars

A new empirical mass-luminosity relation for Main-Sequence. stars in the range −0.6<logm<+0.1 is derived. The sample selected for computations is a merger of visual doubles and spectroscopic binaries, all of them with minor observational errors. To these measures linear and secondorder fits were applied; their r.m.s. errors are ±0.3 in magnitude and ±0.025 in logarithm of the stellar mass. An application to the luminosity function of nearby stars is then presented.

Galactic evolution with bimodal star formation. II. Expectations and problems

AbstractBimodal star formation is an interesting hypothesis from the point of view of galactic evolution. It is believed that bimodal star formation scenarios provide answers to several outstanding problems. In this paper the question is discussed whether by means of LARSON's (1986) bimodal IMF the chemical evolution (D, He, Fe), the nature of the dark matter, the luminosity function of white dwarfs, and the structure in the field star luminosity function in the solar neighborhood can be explained simultaneously.

The infrared luminosity function for low-mass stars

Determination des fonctions de luminosite infrarouge pour des etoiles naines de type M du Pole Galactique Sud et de l'amas des Hyades. Une compilation de donnees photometriques deja publiees et de nouvelles observations est presentee. Les diagrammes a 2 couleurs permettent d'etudier les effets de gravite et de metallicite

OPTICAL ANALYSIS OF AN X-RAY-SELECTED SAMPLE OF STARS

I analyze an X-ray-selected sample of 128 late-type (F-M) stars. These stars were identified as optical counterparts to serendipitous X-ray detections made by the Einstein Observatory Extended Medium Sensitivity Survey. Once identified as X-ray sources, the stars were reobserved with an extensive program of optical observations consisting of highand low-resolution spectroscopy and photometry. Spectral types, luminosity classes, absolute magnitudes, distances, X-ray luminosities, projected rotation rates (v sin i), radial velocities, and binary status have been determined for the sample. I find that Lx is correlated with v sin i for single stars. However, Lx does not correlate with il sin i , which leads me to believe that the correlation seen with v sin i is actually a correlation with radius. Indeed, Lx correlates strongly with radius (color, mass) for main-sequence stars. This result provides a plausibility argument for rotational saturation in the coronae of late-type stars. Since this sample is flux limited, I use sky coverage and sensitivity information from the Einstein Observatory to calculate the end of the X-ray luminosity function for late-type stars. It appears that previously-calculated luminosity functions from optically selected samples have underestimated the number of X-ray F and G dwarfs. I have also discovered eight previously uncataloged M dwarfs within 25 pc of the Sun. My sample includes only M dwarfs of spectral type M5 and earlier, 93% of which are emission stars (i.e., type Me V), as well as two pre-main-sequence M stars. Arguments involving kinematics and stellar rotational velocities are used to estimate the age of these X-ray bright M dwarfs; they appear to be quite young (^ 1-3 X 109 yrs). Since the local space density of X-ray bright M dwarfs increases with mass, I infer a longer activity time scale for lower masses. M dwarfs later than M5 lie below the X-ray sensitivity limit of the sample. An upper limit of logLx = 27.45 is put on their coronal emission.

Wielen dip and IMF for the solar neighborhood stars

The Wielen dip at Mv ⋍ 7 in the Wielen (1974) luminosity function (LF) for the solar neighborhood stars yields a corresponding dip at m ≈ 0.7mo in the present day mass function (PDMF) of main sequence (MS) stars. This Wielen dip suggests that two different initial mass functions (IMF) have been operative after the initial phase of disk evolution and the age of the solar neighborhood is about 13 billion years.

A model for the infrared emission from the bulge of our Galaxy

view Abstract Citations (35) References (6) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Model for the Emission from the Bulge of Our Galaxy Rowan-Robinson, M. ; Chester, T. Abstract A quantitative model for the IR emission from the bulge of the Galaxy is constructed using a sequence of models for circumstellar dust shells around late-type stars. The luminosity function for asymptotic giant branch stars and the distribution function for the dust-shell optical depth are derived. The total bolometric luminosity of the bulge population is 170 million solar luminosities and the total mass loss rate is 0.0083 solar mass/yr. The 12 microns and most of the 25 microns flux from the inner part of M31 can be understood as emission from a bulge population similar to that in the Galaxy. A simple model for the IR emission from late-type stars in the disk of the Galaxy is also given. Publication: The Astrophysical Journal Pub Date: February 1987 DOI: 10.1086/164979 Bibcode: 1987ApJ...313..413R Keywords: Andromeda Galaxy; Astronomical Models; Emission Spectra; Galactic Bulge; Galactic Structure; Infrared Spectra; Stellar Envelopes; Asymptotic Giant Branch Stars; Giant Stars; Late Stars; Optical Thickness; Stellar Luminosity; Stellar Mass Ejection; Astrophysics; GALAXIES: THE GALAXY; GALAXIES: STRUCTURE; INFRARED: SOURCES; STARS: CIRCUMSTELLAR SHELLS full text sources ADS | data products SIMBAD (1) NED (1)

Bimodal Star Formation and Remnant-Dominated Galactic Models

Current data on the luminosity function of nearby stars allow the possibility that the stellar initial mass function (IMF) is double-peaked and that the star formation rate (SFR) has decreased substantially with time. It is then possible to account for all of the unseen mass in the solar vicinity as stellar remnants. A model for the solar neighborhood has been constructed in which the IMF is bimodal, the SFR is constant for the low-mass mode and strongly decreasing for the high-mass mode, and the mass in remnants is equal to the column density of unseen matter; this model is found to be consistent with all of the available constraints on the evolution and stellar content of the solar neighborhood. In particular, the observed chemical evolution is satisfactorily reproduced without infall. The total SFR in the model decreases roughly with the 1.4 power of the gas content, which is more plausible than the nearly constant SFR required by models with a monotonic IMF.

Energy spectrum of flares of UV cet stars and the physical meaning of some statistical characteristics of such stars

On the basis of the observed power-law energy spectrum of the flares of stars of teh UV Cet type, some statistical characteristics of the activity of such stars are considered. It is shown that the mean amplitude of the flares is determined primarily by the amplitude of the weakest flare detected in the given star so that the mean amplitude cannot serve as a measure of the flare activity of the star. The mean frequency of flares detected in flare stars depends on the absolute magnitude of the star and this dependence is determined both by the change in the threshold of flare detection as well as by the real changes in the activity level. The catalog of Haro, Chavira and Gonzalez of flare stars in the Pleiades was used to construct the luminosity function of such stars in this cluster.

Luminosity functions for asymptotic giant branch stars

To understand the evolution of carbon and oxygen rich asymptotic giant branch (AGB) stars it is important to observationally establish the relations between parameters such as luminosity, age, and metallicity. The existence of luminous (brighter than the top of the first giant branch) AGB stars in clusters in the Magellanic Clouds (Mould and Aaronson 1979; Frogel, et al. 1980) provides a nearly ideal situation in which these relations can be determined. Although metallicities and main sequence turn-off ages are known for only a fraction of the clusters, the ranking scheme devised by Searle, et al. (1980; SWB) indicates that age and metallicity are closely related to one another.

The magellanic irregular galaxy DDO 155

The Magellanic irregular galaxy, DDO 50 (= Ho II = A 813+70 = VII Zw 223 = Arp 268), is usually assumed to be a member of the M 81 group. De Vaucouleurs (1979) has derived the distance modulus of the galaxy, μ o = 27.79, from magnitudes of the brightest blue supergiants and brightest red variable given by Sandage and Tammann (1974). The estimated absolute magnitude of the galaxy, M T = −17.04, is close to that of the SMC. We have used B and V plates to obtain a colour-magnitude diagram for this galaxy. We have also obtained further estimates of the distance modulus: first, from measurements of the sizes of H II rings in the galaxy from a deep Hα plate, and second, from a comparison of the luminosity function of the brightest blue stars with the corresponding luminosity function for the SMC.

Solar and late-type dwarfs

The Einstein Observatory and the IUE satellite have provided the observational basis for a major restructuring in theories of coronal formation for late-type stars. For the first time, coronal and transition region emission from a large sample of low mass (1 Mo) dwarf stars has been directly observed, with the unexpected result that essentially all such stars are x-ray emitters. The Sun, which was previously assumed to be typical, is now known to be at the low end of the x-ray luminosity function for solar-type stars. K- and M-dwarfs are observed to have nearly the same luminosity distributions as G-dwarfs and all of these spectral types have a large spread in x-ray luminosity.Observationally, there is a strong correlation between the strength of coronal emission in stars with outer convective zones and the rotation rates of these stars. At the present time we have only the beginnings of a satisfactory theoretical explanation for this correlation; although we are beginning to understand the connection between coronal emission strength and the magnetic field, we do not yet understand the stellar dynamo which generates the magnetic field. Studies of the coronal emission of stars may lead to a better understanding of stellar dynamos.

Stellarstatistische Untersuchungen in der Sonnenumgebung

AbstractSpace densities for stars given in the „Catalogue of nearby stars”︁ and in „Nearby star data published 1969—1978”︁ were calculated for the stellar groups listed in Table 1 as a function of the distance from the galactic plane. The stars are symmetrically distributed with respect to the galactic plane. Space densities for giant stars nearer than 22 pc were also computed. The comparison between the luminosity functions of stars nearer than 5 pc and 22 pc shows that the number of M dwarfs up to 22 pc is given uncompletely.

A comparison of observed and theoretical luminosity functions of carbon stars and late M giants

view Abstract Citations (19) References (50) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A comparison of observed and theoretical luminosity functions of carbon stars and late M giants Miller, G. E. ; Scalo, J. M. Abstract Simulated populations of double-shell phase stellar models undergoing mixing due to helium shell flashes are compared with observations of carbon stars and M giants in the Galaxy, the LMC, the SMC, and the Fornax dwarf galaxy. The available observational constraints for C stars and late M giants in these objects is summarized, and the simulation technique and parametrized mixing model employed is briefly described. The main parameters for which simulation results are obtained are the metal abundance, the fraction of intershell carbon mixed up per flash, the minimum core mass at which mixing begins, the core mass above which mixing does not occur, and the duration of star formation. It is found that the observed variation of the C/M ratio with metal abundance can be accounted for in just about any model for mixing, nearly independently of parameters. The observed C/M variation is, however, a potential probe of metal abundances and their spatial variation in nearby galaxies. Publication: The Astrophysical Journal Pub Date: December 1982 DOI: 10.1086/160500 Bibcode: 1982ApJ...263..259M Keywords: Carbon Stars; Giant Stars; Late Stars; M Stars; Stellar Luminosity; Abundance; Computerized Simulation; Metals; Milky Way Galaxy; Stellar Models; Stellar Structure; Astrophysics full text sources ADS |

An unbiased survey of field star X-ray emission

To determine the X-ray luminosity function of normal stars, 1700 stars brighter than 10th magnitude were surveyed by the imaging proportional counter aboard the Einstein Observatory. Seventy star positions were found to contain excess X-ray counting rates. The number of stars per square degree in a number of magnitude intervals was calculated as a function of spectral type and luminosity class, and the total number of stars for each spectral type brighter than magnitude 9.5 derived in this manner was compared with the 1700-star sample. The agreement is good, as is that between the surface density of soft X-ray sources and the number of stellar emitters predicted from the field star survey. It is concluded that stars probably do not contribute significantly to the diffuse soft X-ray background. The findings are consistent with the notion that stellar age and/or rotation velocity are important determinants of stellar X-ray emission level.

A star of very low luminosity

The method of photometric parallax (MV/V – I relation) has been applied to a UK Schmidt Telescope field towards the South Galactic Pole to derive a kinematically unbiased luminosity function for low mass stars. We present here the discovery of one such star, RG0050–2722, which has an absolute magnitude |$M_V \approx +19$|⁠, and is 25±6 pc from the Sun. This is only the second star known to have |$M_V \geqslant +18$|⁠.

Studies of luminous stars in nearby galaxies. V - The local group irregulars NGC 6822 and IC 1613

view Abstract Citations (56) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Studies of luminous stars in nearby galaxies. V. The local group irregulars NGC 6822 and IC 1613. Humphreys, R. M. Abstract Spectroscopic and photometric observations have been obtained of the brightest stars in the dwarf irregular galaxies NGC 6822 and IC 1613 in the Local Group. The brightest blue stars have visual luminosities of approximately -8.5 mag and -8.2 mag in NGC 6822 and IC 1613, respectively. The brightest M supergiant occurs at a visual luminosity of about -8 mag in each of these galaxies. These results confirm the proposal by Sandage and Tammann (1974) that the luminosities of the brightest blue stars depend on the luminosity of the parent galaxy while the maximum luminosity of the brightest red stars is independent of galaxy type. A discussion of the relative populations of luminous blue and red stars in the H-R diagrams suggests that a steeper luminosity function is responsible for the small numbers of luminous blue stars in these low-luminosity irregular galaxies when compared with the supergiant populations in the Galaxy and LMC. The luminosity function for massive stars in a galaxy would have to be sufficiently steep to not produce any stars or very few stars greater than 40 solar masses to invalidate the calibration of the brightest red supergiants at a visual luminosity of about -8 mag. Publication: The Astrophysical Journal Pub Date: May 1980 DOI: 10.1086/157958 Bibcode: 1980ApJ...238...65H Keywords: Astronomical Catalogs; Local Group (Astronomy); Stellar Luminosity; Stellar Spectrophotometry; Supergiant Stars; Colorimetry; Hertzsprung-Russell Diagram; Interstellar Extinction; M Stars; Supermassive Stars; Variable Stars; Astronomy full text sources ADS | data products SIMBAD (46) NED (6) Related Materials (7) Part 1: 1978ApJS...38..309H Part 2: 1979ApJS...39..389H Part 3: 1979ApJ...232..409H Part 4: 1979ApJ...234..854H Part 6: 1980ApJ...241..587H Part 7: 1980ApJ...241..598H Part 8: 1983ApJ...265..176H