scholarly journals A Search for Main-Sequence Binaries in Globular Clusters

1980 ◽  
Vol 85 ◽  
pp. 357-359 ◽  
Author(s):  
Martha H. Liller
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Eclipsing Binaries ◽  
Cluster Center ◽  
Distance Modulus ◽  
List Type ◽  
Galactic Latitude ◽  
Plate Material ◽  
Evolved Stars ◽  
Visual Distance

It is becoming increasingly clear that no (or only one or two) binaries occur among the evolved stars in globular clusters. Therefore, if binaries exist at all in these systems, they must be found on or near the main sequence. I have chosen 6 clusters to search for faint eclipsing binaries by the following criteria: (1)the apparent visual distance modulus (Harris 1976) (m-M)V ≤ 14.5 mag;(2)the Peterson and King (1975) concentration class c ≤ 1.5, so that the search can be conducted near or at the cluster center where binaries would most likely be found; and(3)the galactic latitude is sufficiently large to avoid problems of extreme contamination by field stars. The clusters thus chosen are NGC3201, 5139 (Omega Cen), 6121 (M4), 6218 (M12), 6254 (M10), and 6809 (M55). The plate material obtained on three nights with the 4-m telescope at CTIO in 1979, consists of seven to nine plates of each cluster on IIIa-F emulsion with an RG610 filter; the search is being conducted with a blink microscope.

Absolute parameters of three southern eclipsing binaries: DQ Car, BK Ind, and V4396 Sgr

2020 ◽  
Vol 493 (2) ◽  
pp. 2659-2675
Author(s):  
Derya Sürgit ◽  
Ahmet Erdem ◽  
Chris A Engelbrecht ◽  
Fred Marang
Keyword(s):  
South African ◽  
Binary Stars ◽  
Main Sequence ◽  
Interstellar Extinction ◽  
Eclipsing Binaries ◽  
Evolutionary Status ◽  
Distance Modulus ◽  
Main Sequence Stars ◽  
The Masses ◽  
Absolute Parameters

ABSTRACT We present combined photometric and spectroscopic analyses of the three southern eclipsing binary stars: DQ Car, BK Ind, and V4396 Sgr. Radial velocity curves of these three systems were obtained at the South African Astronomical Observatory, and their light curves from the available data bases and surveys were used for the analysis. 75 new times of minima for these three eclipsing binaries were derived, and their ephemerides were updated. Only the O–C diagram of DQ Car indicates a cyclical variation, which was interpreted in terms of the light-time effect due to a third body in the system. Our final models describe these three systems as Algol-like binary stars with detached configurations. The masses and radii were found to be M1 = 1.86(±0.17) M⊙, R1 = 1.63(±0.06) R⊙ and M2 = 1.74(±0.17) M⊙, R2 = 1.52(±0.07) R⊙ for the primary and secondary components of DQ Car; M1 = 1.16(±0.05) M⊙, R1 = 1.33(±0.03) R⊙ and M2 = 0.98(±0.04) M⊙, R2 = 1.00(±0.03) R⊙ for BK Ind; and M1 = 3.14(±0.22) M⊙, R1 = 3.00(±0.09) R⊙ and M2 = 3.13(±0.24) M⊙, R2 = 2.40(±0.08) R⊙ for V4396 Sgr, respectively. The distances to DQ Car, BK Ind, and V4396 Sgr were derived to be 701(±50), 285(±20), and 414(±30) pc from the distance modulus formula, taking into account interstellar extinction. The evolutionary status of these three systems was also studied. It has been found that the components of DQ Car are very young stars at the age of ∼25 Myr and those of BK Ind and V4396 Sgr are evolved main-sequence stars at the ages of ∼2.69 Gyr and ∼204 Myr, respectively.

scholarly journals Globular cluster ages from main sequence fitting and detached, eclipsing binaries: The case of 47 Tuc

2008 ◽  
Vol 4 (S258) ◽  
pp. 171-176 ◽  
Author(s):  
Aaron Dotter ◽  
Janusz Kaluzny ◽  
Ian B. Thompson
Keyword(s):  
Stellar Evolution ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Main Sequence ◽  
Eclipsing Binaries ◽  
Eclipsing Binary ◽  
Age Constraints

AbstractAge constraints are most often placed on globular clusters by comparing their CMDs with theoretical isochrones. The recent discoveries of detached, eclipsing binaries in such systems by the Cluster AgeS Experiment (CASE) provide new insights into their ages and, at the same time, provide much-needed tests of stellar evolution models. We describe efforts to model the properties of the detached, eclipsing binary V69 in 47 Tuc and compare age constraints derived from stellar evolution models of V69A and B with ages obtained from fitting isochrones to the cluster CMD. We determine whether or not, under reasonable assumptions of distance, reddening, and metallicity, it is possible to simultaneously constrain the age and He content of 47 Tuc.

scholarly journals On the Origin of the Algol Systems

1968 ◽  
Vol 1 ◽  
pp. 396-408
Author(s):  
M. Plavec
Keyword(s):  
Spectral Type ◽  
Main Sequence ◽  
Eclipsing Binaries ◽  
List Type ◽  
Type Number ◽  
Main Sequence Stars ◽  
Maximum Light ◽  
Spectral Class ◽  
Lagrangian Surfaces ◽  
Visual Binaries

The 4th edition of the Finding List for Observers of Eclipsing Variables (Koch et al, 1963) contains 145 sufficiently well-observed eclipsing binaries brighter than 8·5m at maximum light. Among them, 59 binaries, or 41%, are systems with both components on the main sequence. The second largest group, 52 binaries or 36% of all systems, are systems similar to Algol. These can be characterized as follows: (1)The primary (more massive) components are main-sequence stars, fitting well into the mass-luminosity relation defined by visual binaries and by eclipsing binaries with both components on the main sequence (detached systems).(2)The secondary components are of later spectral type than the primaries, and can be best characterized as subgiants. They are overluminous for their mass as well as for their spectral class.(3)As a rule, the secondary components fill their respective critical Roche lobes (innermost Lagrangian surfaces).

Inhomogeneities in Globular Clusters

1991 ◽  
Vol 9 (1) ◽  
pp. 37-40 ◽  
Author(s):  
Mun-Suk Chun
Keyword(s):  
Globular Clusters ◽  
Large Scale ◽  
Structural Variation ◽  
Main Sequence ◽  
Early Stage ◽  
Observational Evidence ◽  
Chemical Abundance ◽  
Colour Variation ◽  
Evolved Stars ◽  
Colour Gradient

AbstractInhomogeneities in globular clusters are reviewed with the observational evidence for chemical abundance variations from star to star in individual clusters and the large-scale structural variation of clusters. The reality of the radial colour gradient is tested in 47 Tuc (NGC 104). The result shows that the observed radial colour gradient comes from the integration of the calculated colours of individual stars. The cause of this radial colour variation is the result of the concentration of evolved stars and the reddening of the main sequence in the central region. We propose that the CNO abundance gradient in the early stage of a cluster’s formation is the interpretation of the observed radial colour gradient.

scholarly journals A Photoelectric Investigation of the Eclipsing Binary V 78 in Omega Centauri (NGC 5139)

1971 ◽  
Vol 15 ◽  
pp. 235-237
Author(s):  
Edward H. Geyer
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Variable Star ◽  
Eclipsing Binaries ◽  
Stellar Systems ◽  
Light Elements ◽  
Eclipsing Binary ◽  
Evolved Stars ◽  
Photographic Photometry ◽  
Highly Evolved

The existence of eclipsing binaries, though extremely rare, in stellar systems like globular clusters, should attract the observers, because one could obtain fundamental data on highly evolved stars. The variable star V 78 in the globular cluster NGC 5139, which was found by BAILEY (1901), is one of these rare cases. MARTIN (1938) derived the period P = 1ḍ168118, and showed by means of an extensive photographic photometry that it is an Algol type eclipsing binary. Recently SISTERO et al. (1968, 1969) rediscussed the observations of MARTIN, and with additional measurements derived the following light elements:

scholarly journals Variability of ω Centauri Blue Stragglers: Clues to their Origin

1988 ◽  
Vol 126 ◽  
pp. 681-682
Author(s):  
G. S. Da Costa ◽  
John Norris
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Galactic Disk ◽  
Close Binaries ◽  
Blue Stragglers ◽  
The Core ◽  
Evolved Stars ◽  
Internal Mixing ◽  
Residual Gas ◽  
Lifetime Extension

The four possible origins usually discussed for blue stragglers in stellar systems are (a) mass transfer in, or coalescence of, close binaries; (b) main sequence lifetime extension either through internal mixing or high non-thermal pressures; (c) complete mixing events in evolved stars at the core helium flash; and (d) ongoing star formation over long intervals. However, alternative (d) can be ruled out for the case of globular clusters because any residual gas in the cluster is very efficiently swept out as the cluster passes through the galactic disk, an event that occurs approximately every hundred million years. Hypotheses (a) and (b) both predict masses for the blue stragglers that exceed the turnoff mass but if alternative (c) is correct, then the blue stragglers should have masses less than or equal to the turnoff mass.

scholarly journals Discovery of Infrared Stars in Globular Clusters in the Magellanic Clouds and Their Light Variations

1998 ◽  
Vol 11 (1) ◽  
pp. 395-395
Author(s):  
S. Nishida ◽  
T. Tanabé ◽  
S. Matsumoto ◽  
T. Onaka ◽  
Y. Nakada ◽  
...  
Keyword(s):  
Mass Loss ◽  
Globular Clusters ◽  
Main Sequence ◽  
Near Infrared ◽  
Magellanic Clouds ◽  
Infrared Light ◽  
Agb Stars ◽  
Dust Shells ◽  
Infrared Stars ◽  
Infrared Survey

A systematic near-infrared survey was made for globular clusters in the Magellanic Clouds. Two infrared stars were discovered in NGC419 (SMC) and NGC1783 (LMC). NGC419 and NGC1783 are well-studied rich globular clusters whose turn-off masses and ages are estimated MTO ~ 2.0 Mʘ and т ~1.2 Gyr for NGC419, and MT0 ~ 2.0 Mʘ and т ʘ 0.9 Gyr for NGC1783, respectively. The periods of the infrared light variations were determined to be 540 dfor NGC419IR1 and to be 480 d for NGC1783IR1, respectively. Comparison of the measurements with the period—if magnitude relation for carbon Miras in the LMC by Groenewegen and Whitelock(1996) revealed that the Kmagnitudes of the infrared stars were fainter by about 0.3 — 0.8 magnitude than those predicted by the P — K relation. This deviation can be explained if the infrared stars are surrounded by thick dust shells and are obscured even in the K band. The positions of NGC419IR1and NGC1783IR1 on the P — K diagram suggest that AGB stars with the main sequence masses of about 2 Mʘ start their heavy mass-loss when P ʘ 500 d.

scholarly journals CCD photometry and spectroscopy of 14 IRAS sources having far-IR colours similar to Planetary Nebulae

1997 ◽  
Vol 180 ◽  
pp. 365-365
Author(s):  
B. E. Reddy ◽  
M. Parthasarathy
Keyword(s):  
Spectral Energy Distribution ◽  
Planetary Nebulae ◽  
Spectral Energy ◽  
Galactic Latitude ◽  
Ccd Photometry ◽  
Ccd Imaging ◽  
Evolved Stars ◽  
Molecular Features ◽  
Intense Mass ◽  
Low Mass

CCD imaging and BVRI photometry of 14 IRAS sources with far-IR colours similar to planetary nebulae and post-AGB stars are presented. Also results of optical and near-IR spectroscopy of 10 of these candidates are given. Based on the spectral energy distribution from 0.4 μm to 100 μm, the sample of program stars are put into two groups. The sources IRAS 08187-1905, IRAS 05238-0626 and IRAS 17086-2403 present similar flux distributions. These three sources have detached cold dust components with dust radii Rd ≈ 1000 R∗. The low infrared variability of theses sources suggests that the intense mass loss has been ceased. All three sources are at high galactic latitude (1>9°) suggesting that these are old low-mass evolved stars. In the IRAS colour-colour diagram of Likkel et al (1991) these sources fall in the region where most of the stars are evolved stars and PNe but without CO detection. This is consistent with at least one source IRAS 17086-2403, in which OH and CO molecular features are not detected. The far-IR excess, non-variability and high latitude of these objects suggest that these are post-AGB supergiants, slowly evolving towards planetary nebula phase.

scholarly journals Are sdAs helium core stars?

2017 ◽  
Vol 26 (1) ◽  
Author(s):  
Ingrid Pelisoli ◽  
S. O. Kepler ◽  
Detlev Koester
Keyword(s):  
Main Sequence ◽  
Galactic Disk ◽  
Physical Nature ◽  
Sloan Digital Sky Survey ◽  
Distance Modulus ◽  
Main Sequence Stars ◽  
Sky Survey ◽  
Balmer Lines ◽  
Low Mass ◽  
Binary Evolution

AbstractEvolved stars with a helium core can be formed by non-conservative mass exchange interaction with a companion or by strong mass loss. Their masses are smaller than 0.5 M⊙. In the database of the Sloan Digital Sky Survey (SDSS), there are several thousand stars which were classified by the pipeline as dwarf O, B and A stars. Considering the lifetimes of these classes on the main sequence, and their distance modulus at the SDSS bright saturation, if these were common main sequence stars, there would be a considerable population of young stars very far from the galactic disk. Their spectra are dominated by Balmer lines which suggest effective temperatures around 8 000-10 000 K. Several thousand have significant proper motions, indicative of distances smaller than 1 kpc. Many show surface gravity in intermediate values between main sequence and white dwarf, 4.75 < log g < 6.5, hence they have been called sdA stars. Their physical nature and evolutionary history remains a puzzle. We propose they are not H-core main sequence stars, but helium core stars and the outcomes of binary evolution. We report the discovery of two new extremely-low mass white dwarfs among the sdAs to support this statement.

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