- ID:
- ivo://CDS.VizieR/J/AJ/151/40
- Title:
- Differential BV photometry of 5 variables in M79
- Short Name:
- J/AJ/151/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of a luminous F-type post-asymptotic-giant-branch (PAGB) star in the Galactic globular cluster (GC) M79 (NGC 1904). At visual apparent and absolute magnitudes of V=12.20 and M_V_=-3.46, this "yellow" PAGB star is by a small margin the visually brightest star known in any GC. It was identified using CCD observations in the uBVI photometric system, which is optimized to detect stars with large Balmer discontinuities, indicative of very low surface gravities. Follow-up observations with the SMARTS 1.3 and 1.5m telescopes show that the star is not variable in light or radial velocity, and that its velocity is consistent with cluster membership. Near- and mid-infrared observations with 2MASS and WISE show no evidence for circumstellar dust. We argue that a sharp upper limit to the luminosity function exists for yellow PAGB stars in old populations, making them excellent candidates for Population II standard candles, which are four magnitudes brighter than RR Lyrae variables. Their luminosities are consistent with the stars being in a PAGB evolutionary phase, with core masses of ~0.53M_{sun}_. We also detected four very hot stars lying above the horizontal branch ("AGB-manque" stars); along with the PAGB star, they are the brightest objects in M79 in the near-ultraviolet. In the Appendix, we give periods and light curves for five variables in M79: three RR Lyrae stars, a Type II Cepheid, and a semiregular variable.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/146/146
- Title:
- Differential BV photometry of VV Crv
- Short Name:
- J/AJ/146/146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained red-wavelength spectroscopy and Johnson B and V differential photoelectric photometry of the eclipsing binary VV Crv=HR 4821. The system is the secondary of the common proper motion double star ADS 8627, which has a separation of 5.2". VV Crv has an orbital period of 3.144536 days and a low but non-zero eccentricity of 0.085. With the Wilson-Devinney program we have determined a simultaneous solution of our spectroscopic and photometric observations. Those orbital elements produce masses of M_1_=1.978+/-0.010M_{sun}_ and M_2_=1.513+/-0.008M_{sun}_, and radii of R_1_=3.375+/-0.010R_{sun}_ and R_2_=1.650+/-0.008R_{sun}_for the primary and secondary, respectively. The effective temperatures of the two components are 6500K (fixed) and 6638K, so the star we call the primary is the more massive but cooler and larger component. A comparison with evolutionary tracks indicates that the components are metal rich with [Fe/H]=0.3, and the system has an age of 1.2Gyr. The primary is near the end of its main-sequence lifetime and is rotating significantly faster than its pseudosynchronous velocity. The secondary is still well ensconced on the main sequence and is rotating more slowly than its pseudosynchronous rate.
- ID:
- ivo://CDS.VizieR/J/AJ/145/39
- Title:
- Differential BV(RI)c light curves of PY Vir
- Short Name:
- J/AJ/145/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Complete CCD photometric light curves in BV(RI)_c_ bands obtained in 2012 for the short-period close binary system PY Virginis are presented. A new photometric analysis with the Wilson-Van Hamme code shows that PY Vir is an A-type marginal contact binary system. The absolute parameters of PY Vir are derived using spectroscopic and photometric solutions. Combining new determined times of minimum light with others published in the literature, the O-C diagram of the binary star is investigated. A periodic variation, with a period of 5.22(+/-0.05)years and an amplitude of 0.0075(+/-0.0004)days, was discovered. Since the spectrum of a third component has been detected by Rucinski et al. (2008, cat. J/AJ/136/586), we consider this cyclic period oscillation to be the result of the light-time effect due to the presence of a third body. This third component may also be a binary itself. Therefore, PY Vir should be a quadruple system composed of two cool-type binary systems. This system is a good astrophysical laboratory to study the formation and evolution of close binaries and multiple systems.
- ID:
- ivo://CDS.VizieR/J/AJ/147/50
- Title:
- Differential BVRI light curves of DV Psc
- Short Name:
- J/AJ/147/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present six new BVR_c_I_c_ CCD light curves of a short-period RS CVn binary DV Psc obtained in 2010-2012. The light curve distortions change on both short and long timescales, which is explained by two starspots on the primary component. Moreover, five new flare events were detected and the flare ratio of DV Psc is about 0.082 flares per hour. There is a possible relation between the phases (longitude) of the flares and starspots for all of the available data of late-type binaries, which implies a correlation of the stellar activity of the spots and flares. The cyclic oscillation, with a period of 4.9+/-0.4yr, may result from the magnetic activity cycle, identified by the variability of Max.I-Max.II. Until now, there were no spectroscopic studies of chromospheric activity indicators of the H_{beta}_and H_{gamma}_lines for DV Psc. Our observations of these indicators show that DV Psc is active, with excess emissions. The updated O-C diagram with an observing time span of about 15yr shows an upward parabola, which indicates a secular increase in the orbital period of DV Psc. The orbital period secularly increases at a rate of dP/dt=2.0x10^-7^days/yr, which might be explained by the angular momentum exchanges or mass transfer from the secondary to primary component.
- ID:
- ivo://CDS.VizieR/J/AJ/146/79
- Title:
- Differential BVRI light curves of EP And
- Short Name:
- J/AJ/146/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New multi-color CCD photometric light curves of the eclipsing binary EP And were obtained over six nights in 2006, 2011, and 2012. Using the Wilson-Devinney code, we computed the photometric elements of this system. It was discovered that EP And is a W-type W UMa contact binary system with a mass ratio of q=2.685 and a degree of contact factor f=24.9%, rather than an A-type system. Combining 28 newly determined times of minimum light derived from 1999 to 2012 with others collected from the literature, a long-term increase (dP/dt=+5.22x10^-8^days/yr) with a sinusoidal variation (A=0.0109days; T=40.89yr) in the orbital period was found. The orbital period secular increases may be interpreted as conservative mass transfer from the less massive component to the more massive one, and cyclic variations of the orbital period may be caused by the light-travel time effect through the presence of a third body. The evolutionary status and the age of the system are also discussed.
- ID:
- ivo://CDS.VizieR/J/AJ/145/16
- Title:
- Differential BVRI light curves of NSVS 02502726
- Short Name:
- J/AJ/145/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NSVS 02502726 has been known as a double-lined, detached eclipsing binary that consists of two low-mass stars. We obtained BVRI photometric follow-up observations in 2009 and 2011 to measure improved physical properties of the binary star. Each set of light curves, including the 2008 data given by Cakirli et al., was simultaneously analyzed with the previously published radial velocity curves using the Wilson-Devinney binary code. The conspicuous seasonal light variations of the system are satisfactorily modeled by a two-spot model with one starspot on each component and by changes of the spot parameters with time. Based on 23 eclipse timings calculated from the synthetic model and one ephemeris epoch, an orbital period study of NSVS 02502726 reveals that the period has experienced a continuous decrease of -5.9x10^-7^day/yr or a sinusoidal variation with a period and semi-amplitude of 2.51yr and 0.0011days, respectively. The timing variations could be interpreted as either the light-travel-time effect due to the presence of an unseen third body, or as the combination of this effect and angular momentum loss via magnetic stellar wind braking. Individual masses and radii of both components are determined to be M_1_=0.689+/-0.016M_{sun}_, M_2_=0.341+/-0.009M_{sun}_, R_1_=0.707+/-0.007R_{sun}_, and R_2_=0.657+/-0.008R_{sun}_. The results are very different from those of Cakirli et al. with the primary's radius (0.674+/-0.006R_{sun}_) smaller the secondary's (0.763+/-0.007R_{sun}_). We compared the physical parameters presented in this paper with current low-mass stellar models and found that the measured values of the primary star are best fitted to a 79Myr isochrone. The primary is in good agreement with the empirical mass-radius relation from low-mass binaries, but the secondary is oversized by about 85%.
- ID:
- ivo://CDS.VizieR/J/AJ/146/157
- Title:
- Differential BVRI photometry of FI Boo
- Short Name:
- J/AJ/146/157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed analysis of the interesting W UMa binary FI Boo in view of the spectroscopic signature of a third body through photometry, period variation, and a thorough investigation of solution uniqueness. We obtained new BVR_c_I_c_ photometric data that, when combined with spectroscopic data, enable us to analyze the system FI Boo and determine its basic orbital and physical properties through PHOEBE, as well as the period variation by studying the times of the minima. This combined approach allows us to study the long-term period changes in the system for the first time in order to investigate the presence of a third body and to check extensively the solution uniqueness and the uncertainties of derived parameters. Our modeling indicates that FI Boo is a W-type moderate (f=50.15%+/-8.10%) overcontact binary with component masses of M_h_=0.40+/-0.05M_{sun}_ and M_c_=1.07+/-0.05M_{sun}_, temperatures of T_h_=5746+/-33K and T_c_=5420+/-56K, and a third body, which may play an important role in the formation and evolution. The results were tested by heuristic scanning and parameter kicking to provide the consistent and reliable set of parameters that was used to obtain the initial masses of the progenitors (1.71+/-0.10M_{sun}_ and 0.63+/-0.01M_{sun}_, respectively). We also investigated the evolutionary status of massive components with several sets of widely used isochrones.
- ID:
- ivo://CDS.VizieR/J/AJ/149/194
- Title:
- Differential BVR light curves of DK Cyg
- Short Name:
- J/AJ/149/194
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New CCD photometry is presented for the hot overcontact binary DK Cyg together with reasonable explanations for the light and period variations. Historical light and velocity curves from 1962 to 2012 were simultaneously analyzed with the Wilson-Devinney (W-D) synthesis code. The brightness disturbances were satisfactorily modeled by applying a magnetic cool spot on the primary star. Based on 261 times of minimum light that include 116 new timings and span more than 87 years, a period study reveals that the orbital period has varied due to a periodic oscillation superimposed on an upward parabola. The period and semi-amplitude of the modulation are about 78.1years and 0.0037days, respectively. This detail is interpreted as a light-travel-time effect due to a circumbinary companion with a minimum mass of M_3_=0.065M_{sun}_, within the theoretical limit of ~0.07M_{sun}_ for a brown dwarf star. The observed period increase at a fractional rate of +2.74x10^-10^ is in excellent agreement with that calculated from our W-D synthesis. Mass transfer from the secondary to the primary component is mainly responsible for the secular period change. We examined the evolutionary status of the DK Cyg system from the absolute dimensions.
- ID:
- ivo://CDS.VizieR/J/AJ/145/100
- Title:
- Differential BVR light curves of EP And
- Short Name:
- J/AJ/145/100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new long-term CCD photometry for EP And acquired during the period 2007-2012. The light curves display total eclipses at primary minima and season-to-season light variability. Our synthesis for all available light curves indicates that the eclipsing pair is a W-type overcontact binary with parameters of q=2.578, i=83.3{deg}, {Delta}T=27K, f=28%, and l_3_=2%-3%. The asymmetric light curves in 2007 were satisfactorily modeled by a cool spot on either of the eclipsing components from a magnetic dynamo. Including our 95 timing measurements, a total of 414 times of minimum light spanning about 82yr was used for a period study. A detailed analysis of the eclipse timing diagram revealed that the orbital period of EP And has varied as a combination of an upward-opening parabola and two periodic variations, with cycle lengths of P_3_=44.6yr and P_4_=1.834yr and semi-amplitudes of K_3_=0.0100days and K_4_=0.0039days, respectively. The observed period increase at a fractional rate of +1.39*10^-10^ is in excellent agreement with that calculated from the W-D code and can be plausibly explained by some combination of mass transfer from the primary to the secondary star and angular momentum loss due to magnetic braking. The most reasonable explanation for both cycles is a pair of light-travel-time effects driven by the possible existence of a third and fourth component with projected masses of M_3_=0.25M_{sun}_ and M_4_=0.90M_{sun}_. The more massive companion could be revealed using high-resolution spectroscopic data extending over the course of a few years and could also be a binary itself. It is possible that the circumbinary objects may have played an important role in the formation and evolution of the eclipsing pair, which would cause it to have a short initial orbital period and thus evolve into an overcontact configuration by angular momentum loss.
- ID:
- ivo://CDS.VizieR/J/AJ/147/91
- Title:
- Differential BVR light curves of V407 Peg
- Short Name:
- J/AJ/147/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New multiband CCD photometry is presented for V407 Peg; the R_C_ light curves are the first ever compiled. Our light curves, displaying a flat bottom at secondary minimum and an O'Connell effect, were simultaneously analyzed with the radial velocity (RV) curves given by Rucinski et al. The light changes of the system are best modeled using both a hot spot on the secondary star and a third light. The model also represents historical light curves. All available minimum epochs, including our six timing measurements, have been examined and they indicate that the eclipse timing variation is mainly caused by light asymmetries due to the spot activity detected in the light-curve synthesis. The hot spot may be produced as a result of the impact of the gas stream from the primary star. Our light and velocity solutions indicate that V407 Peg is a totally eclipsing A-type overcontact binary with values of q=0.251, i=87.6{deg}, {Delta}T=496K, f=61%, and l_3_=11~16%. Individual masses and radii of both components are determined to be M_1_=1.72M_{sun}_, M_2_=0.43M_{sun}_, R_1_=2.15R_{sun}_, and R_2_=1.21R_{sun}_. These results are very different from previous ones, which is probably caused by the light curves with distorted and inclined eclipses used in those other analyses. The fact that there are no objects optically related to the system and that the seasonal RVs show a large discrepancy in systemic velocity indicates that the third light source most likely arises from a tertiary component orbiting the eclipsing pair.
