Unevolved Main-sequence Stars Research Articles

PIXEL COLOR MAGNITUDE DIAGRAMS FOR SEMI-RESOLVED STELLAR POPULATIONS: THE STAR FORMATION HISTORY OF REGIONS WITHIN THE DISK AND BULGE OF M31

ABSTRACT The analysis of stellar populations has, by and large, been developed for two limiting cases: spatially resolved stellar populations in the color–magnitude diagram, and integrated light observations of distant systems. In between these two extremes lies the semi-resolved regime, which encompasses a rich and relatively unexplored realm of observational phenomena. Here we develop the concept of pixel color–magnitude diagrams (pCMDs) as a powerful technique for analyzing stellar populations in the semi-resolved regime. pCMDs show the distribution of imaging data in the plane of pixel luminosity versus pixel color. A key feature of pCMDs is that they are sensitive to all stars, including both the evolved giants and the unevolved main sequence stars. An important variable in this regime is the mean number of stars per pixel, . Simulated pCMDs demonstrate a strong sensitivity to the star formation history (SFH) and have the potential to break degeneracies between age, metallicity and dust based on two filter data for values of up to at least 104. We extract pCMDs from Hubble Space Telescope optical imaging of M31 and derive SFHs with seven independent age bins from 106 to 1010 year for both the crowded disk and bulge regions (where ). From analyzing a small region of the disk we find a SFH that is smooth and consistent with an exponential decay timescale of 4 Gyr. The bulge SFH is also smooth and consistent with a 2 Gyr decay timescale. pCMDs will likely play an important role in maximizing the science returns from next generation ground and space-based facilities.

Absolute parameters of southern eclipsing binary: MW Pup

This paper presents the first analysis of spectroscopic and photometric observations of the southern eclipsing binary star MW Pup. ASAS V light and SAAO radial velocity curves of the system were solved simultaneously using Wilson–Devinney code. The results describe MW Pup as an Algol-like binary star with a detached configuration. The masses of the components were found to be 2.20±0.06 and 1.88±0.07M⊙ and the radii to be 1.84±0.03 and 1.72±0.03R⊙ for primary and secondary components, respectively. The distance to MW Pup was calculated to be 430±30pc from the dynamic parallax, neglecting interstellar absorption, in agreement with the value derived from the eclipse-parallax method. The evolution of the system is also discussed. Both components are unevolved Main Sequence stars and the dynamic age of the system is estimated as 263±70My when compared to theoretical evolution models.

WASP-3b: a strongly irradiated transiting gas-giant planet

We report the discovery of WASP-3b, the third transiting exoplanet to be discovered by the WASP and SOPHIE collaboration. WASP-3b transits its host star USNO-B1.0 1256−0285133 every 1.846 834 ± 0.000 002 d. Our high-precision radial velocity measurements present a variation with amplitude characteristic of a planetary-mass companion and in phase with the light curve. Adaptive optics imaging shows no evidence for nearby stellar companions, and line-bisector analysis excludes faint, unresolved binarity and stellar activity as the cause of the radial velocity variations. We make a preliminary spectroscopic analysis of the host star and find it to have T eff = 6400 ± 100 K and log g = 4.25 ± 0.05 which suggests it is most likely an unevolved main-sequence star of spectral type F7-8V. Our simultaneous modelling of the transit photometry and reflex motion of the host leads us to derive a mass of 1.76 +0.08 −0.14 MJ and radius 1.31 +0.07 −0.14 RJ for WASP-3b. The proximity and relative temperature of the host star suggests that WASP-3b is one of the hottest exoplanets known, and thus has the potential to place stringent constraints on exoplanet atmospheric models.

Globular Cluster Giant Branch Luminosity Functions: “Extra Stars” and “Deep Mixing”

We explore the possibility that is the reason that there are red giants in the Galactic globular clusters M5 and M30. Deep mixing has often been invoked to account for the abundance anomalies observed in many bright Galactic globular cluster giants. Here we assume that it also adds fuel to the hydrogen-burning shell of a typical giant in some clusters and returns helium to the envelope above. We use a simple mixing model to estimate how much fuel has been added to the hydrogen-burning shell of a typical red giant in M5 and M30 from the number of stars in the red giant branch (RGB) luminosity functions for these two clusters. Presumably, red giants are common in Galactic globular clusters. M5 and M30 were chosen solely because the available luminosity functions for both were derived from an exceptionally large sample of stars in two colors: the RGB luminosity functions are especially well defined and well normalized to unevolved main-sequence stars. If deep mixing is the reason that there are too many M5 giants, the number of giants suggests that the envelope of a typical M5 star should be significantly enriched in helium (ΔY ≈ 0.07) by the time it reaches the tip of the giant branch. Hence, deep mixing may be (at least part of) the reason that M5 has a surprisingly blue horizontal branch (HB) for a moderately metal-rich cluster. If deep mixing occurs and ΔY ≈ 0.07, we can account for part, but only a small part, of the very low value of R—and the surprisingly low estimate for Y—that Sandquist et al. found from their B-band luminosity function. Sandquist et al.'s value of the helium indicator delta suggests that the helium abundance is enhanced (ΔY = 0.04 ± 0.02) in HB stars at the blue edge of the instability strip. If deep mixing accounts for the extra giants that have been observed in M30, Y will be about 0.05 higher in the envelope of a typical M30 HB star than it was when that star left the main sequence. In addition to accounting for the M30 giants, deep mixing can give a good account of (1) the lack of a on the RGB or the presence of a small bump in the wrong place, (2) the surprisingly bright horizontal branch, and (3) the anomalous values of both Δ and R. The abundances of the light elements suggest that deep mixing is much more common in some clusters than in others and more extensive in some stars in a cluster than in others. If deep mixing does add fuel to evolving giants in some clusters, there are many interesting ramifications. For example, all horizontal branches may not have been created equal; some might well be brighter than others. Sweigart and Sweigart & Catelan have recently described how mixing helium out into the envelope of a red giant may solve a number of cluster blue star mysteries. We point out a number of additional mysteries that might be solved by looking at the fuel that is mixed down into the hydrogen-burning shell: e.g., the large range in the values that have been observed for R (the ratio of bright giants to HB stars), the observed range in the helium estimator Δ at a constant metallicity, and the variations observed in the RGB bumps among otherwise similar clusters.

The chemical compositions and ages of globular clusters

Recent technological advances have led to a dramatic improvement in the quality of photometric and spectroscopic data obtainable on stars in globular clusters. Evidence from CCD-based colour magnitude diagrams points to clear differences in age between some clusters. High dispersion spectra show that abundance variations cannot explain the observed differences. In particular, it seems that NGC 288 must be 2–3 Gyr older than NGC 362. The same spectra show that although there is a spread in some molecular band strengths in NGC 362, the total C+N+O abundance remains constant, indicating that the material has undergone varying amounts of nuclear processing. No variations are seen in the abundances of iron group elements. Lower dispersion spectra for a large sample of faint stars in 47 Tucanae, obtained with a multi-object optical fibre system, show that unevolved main sequence stars in that cluster share the same CNO variations as the bright giants. The conclusion from all these data is that the intra-cluster CNO variations are neither truly primordial nor due to evolutionary mixing. It may be that there was a sufficiently extended period of star formation for material from first generation stars to be used in later generations, or that some pollution has occurred due to mass loss. Finally, it is noted that if ‘prehistoric’ clusters exist with ages of around 50 Gyr, as hypothesised in some cosmological models, these should probably still be rather obvious and readily recognised.

The minimum mass ratio of W Ursae Majoris binaries

The minimum mass ratio for tidal stability of a contact binary containing two unevolved main-sequence stars is calculated to be $\qmin\simeq0.09$ in the case of a mostly radiative primary, and is higher if an appreciable fraction of the mass lies in a convective envelope. At least one observed system, AW UMa, has a mass ratio just below this value ($q=0.075$), implying, if the system is stable, that the primary must be slightly evolved and must have a very shallow convective envelope. Contact binaries with mass ratios significantly below that of AW UMa should not be observed, since they are tidally unstable and quickly merge into a single, rapidly rotating object, on a timescale $\sim10^3$--$10^4\,$yr.

HR 2142: A Semi-Detached Interacting Binary?

The energy distribution of HR 2142 is studied in order to test the hypothesis that this star is an interacting binary with a cool Roche–lobe filling companion. We find that, for any reasonable choice of Teff, the companion should have been detected in the red part of the spectrum. We propose instead that the Be star is the outcome of a case B mass-transfer, which has pun it up. It is now surrounded by a mass-loss disc, rather than an accretion disc and is accompanied by either a helium star (resembling the Φ Per system) or by a white dwarf. If the binary was born spinning rapidly, alternatively the companion may be a solar-type, unevolved main sequence star. In case of a Helium star companion, there may be Helium lines visible (like in Φ Per), or the helium star may be detectable in the XUV, e.g. by the ROSAT XUV instrument. A white dwarf companion may be accreting material from the disc around the Be star and may show low luminosity X-ray emission. This emission may have been seen in the ROSAT PSPC X-Ray Survey.

The effect of Main-Sequence stars on age estimates of open clusters

Existing methods for age estimation of open clusters are discussed. Most of the observed open clusters (except extremely young and old) contain 50–90% unevolved Main-Sequence stars. Possible difficulties encountered in estimating the actual age of an unevolved Main-Sequence star are discussed. For a relatively reliable cluster age estimation only a small percentage of cluster members are suitable. The effect of unevolved Main-Sequence stars on open cluster age estimates using the modified method of isochromes is analyzed.

Some Aspects of the Evolutionary Status Of W Ursae Majoris Binaries Deduced from Observational Data

AbstractWe have developed a test for the evolutionary state of W Ursae Majoris binaries by comparing the observed spectral type of 31 of these systems (14 of type W and 17 of type A) with the expected one when their primary component is an unevolved main sequence star. It appears that both the W- and A-type systems have a primary with a mass and radius too large to be compatible with the observed spectral type,so there is no indication that each type should mark a different evolutionary stage.

Some Regularities in Chemical Composition of Unevolved Main Sequence Stars and Synthesis of the Elements

The published data on chemical abundances derived from fine analysis for about 80 G, F and A main sequence stars are analysed. The following conclusions are drawn :

ON the Supermetallicity of the Main-Sequence Stars in M67 and NGC 188

view Abstract Citations (51) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS ON the Supermetallicity of the Main-Sequence Stars in M67 and NGC 188 Spinrad, Hyron ; Greenstein, Jesse L. ; Taylor, Benjamin J. ; King, Ivan R. Abstract To investigate the metal abundances of unevolved main-sequence stars in old open clusters, we have redetermined the interstellar reddening in M67 and NGC 188 by two new techniques. We find (EB - V) from 0.11 to 0.09 mag for M67 and E(B - 17) about 0.15 mag for NGC 188, higher than the reddening values suggested by the photometry of Eggen and Sandage. We have also scanned the Na D4ines in four main-sequence late F stars in M67 with an effective resolution of 14 A; the D-lines are strong-well above the Hyades level. We find [Na/H]0 = +0.5 to +0.6 for these M67 F dwarfs. Fagerholm 81, the B7 V star in M67, has a strong Mg 4481 line; for this star, [Mg/H]0 = +0.6. It has normal helium. Classification of low-dispersion spectra shows spectral anomalies of turnoff-point stars in both M67 and NGC 188. Metallic lines yield later types than do H and H the index of spectral peculiarity (AS = - 4 for M67 and (AS = - 6 for NGC 188. The negative AS indices are strongly suggestive of supermetallicity, the NGC 188 stars being more extreme. The paper concludes with a discussion of the validity of the classical interpretation of small ultraviolet excesses in two-color diagrams of open clusters. Publication: The Astrophysical Journal Pub Date: December 1970 DOI: 10.1086/150718 Bibcode: 1970ApJ...162..891S full text sources ADS | data products SIMBAD (23)

Color-luminosity array for NGC 752

view Abstract Citations (70) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Color-luminosity array for NGC 752. Eggen, O. J. Abstract New observations of stars in and near the cluster NGC 752 have been obtained with the 60- and 200- inch reflectors. The resulting color-magnitude diagram based on stars which have a high probability of membership in the cluster shows a small gap between the evolved and unevolved main-sequence stars. The ultraviolet excesses of the evolved F-type stars are correlated with the values of B - V. The reddest, F-type giants show an ultraviolet deficiency, compared with main-sequence stars, of OWl A search for faint members to VE = 17"' in a small area near the center of the cluster was largely unsuccessful. The region of the cluster contains several stars, more distant than the cluster, with ultraviolet excesses, a(U - B) = + OWl, similar to that found for the cluster stars; these distant objects lie about 250 parsecs above the galactic plane. The color4uminosity array for the cluster is similar in many respects to that for the rich cluster NGC 2477. Publication: The Astrophysical Journal Pub Date: August 1963 DOI: 10.1086/147650 Bibcode: 1963ApJ...138..356E full text sources ADS | data products SIMBAD (2) GCPD (1)