- ID:
- ivo://CDS.VizieR/J/A+A/500/917
- Title:
- Variable stars in LMC MACHO fields 1 & 79
- Short Name:
- J/A+A/500/917
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Because of the strong effect of systematics/trends in variable star observations, we apply the Trend Filtering Algorithm (TFA) to a subset of the MACHO database and search for variable stars. TFA has been applied successfully in planetary transit searches, where weak, short-lasting periodic dimmings are sought in the presence of noise and various systematics (due to, e.g., imperfect flat fielding, crowding, etc). These latter effects introduce colored noise in the photometric time series that can completely overwhelm the signal. By using a large number of available photometric time series of a given field, TFA utilizes the fact that the same types of systematics appear in several/many time series of the same field. As a result, we attempt to reproduce each target time series by a linear combination of templates, optimized by least-squares. After a signal has been identified in the residuals between the original time series and the systematics computed by TFA, we reconstruct the signal by employing the full model, including the signal, systematics and noise. We apply TFA to the brightest ~5300 objects from subsets of each of the MACHO Large Magellanic Cloud fields #1 and #79. We find that the Fourier frequency analysis performed on the original data detects some 60% of the objects as trend-dominated. This figure decreases essentially to zero after using TFA. In total, we detect 387 variables in the two fields, 183 of which would have remained undetected without using TFA. Where possible, we give preliminary classification of the variables found.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/449/164
- Title:
- Variable Stars in MC Clusters. II
- Short Name:
- J/ApJ/449/164
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a study aimed at identifying variable stars in the rich LMC cluster NGC 1850. V and I band CCD imaging spanning more than 5 years in a 10'x10' field surrounding the cluster has allowed us to identify more than 30 variable stars, including seven classical Cepheids, one anomalous Cepheid, two RR Lyrae variables, 19 long-period variables (LPVs), one blue eclipsing binary, one possible pair of eclipsing giants, and several peculiar variables. The only likely cluster member is a Cepheid. Isochrone fitting to the cluster CMD yields an age of 80 Myr if an LMC distance modulus of 18.5 is adopted. A comparison of pulsation and evolution masses for the Cepheids still yields a ratio of evolution to pulsation mass of ~1.2 for evolution models computed with core overshoot parameter Lambda = 0.5, where Lambda = 2d_ov/H_p, d_ov is the distance that convection overshoots beyond the Schwarzschild boundary and H_p is the pressure scale height. An overshoot parameter Lambda ~ 1.0 would be required to bring the evolution and pulsation masses into agreement. One of the Cepheids in the field is a bump Cepheid. A calculation of the bump mass yields a value in reasonable agreement with the pulsation mass. We show that detailed modelling of individual bump Cepheids is capable of providing very tight constraints on the LMC distance modulus. The Cepheid period-luminosity-color relation compared to the theoretical relation yields a LMC distance modulus of 18.60. Finally, arguments are presented which suggest that the LPVs are a mixture of fundamental mode pulsators and small-amplitude overtone pulsators.
- ID:
- ivo://CDS.VizieR/J/AJ/142/107
- Title:
- Variable stars in NGC 1466
- Short Name:
- J/AJ/142/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the first in a series of papers studying the variable stars in Large Magellanic Cloud globular clusters. The primary goal of this series is to better understand how the RR Lyrae stars in Oosterhoff-intermediate systems compare to those in Oosterhoff I/II systems. In this paper, we present the results of our new time-series BV photometric study of NGC 1466. A total of 62 variables were identified in the cluster, of which 16 are new discoveries. The variables include 30 RRab stars, 11 RRc stars, 8 RRd stars, 1 candidate RR Lyrae, 2 long-period variables, 1 potential anomalous Cepheid, and 9 variables of undetermined classification. We present photometric parameters for these variables.
- ID:
- ivo://CDS.VizieR/J/AJ/138/1310
- Title:
- Variable stars in NGC 2257. I.
- Short Name:
- J/AJ/138/1310
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The variable stars in the Large Magellanic Cloud star cluster NGC 2257 are reinvestigated using photometry (to ~20th mag) of over 400 new B, V CCD images taken with the CTIO 0.9m telescope on 14 nights in 2007 December and 2008 January. New period searches have been made using two independent algorithms (CLEAN, Period04); the resultant periods of most of the stars are consistent with the pulsation periods derived previously, and where there are discrepancies these have been resolved. For the B and V light curves, accurate Fourier coefficients and parameters are given. Six new variable stars have been discovered (V45-50), including a bright candidate long-period variable star showing secondary oscillations (V45) and two anomalously bright RRc stars (V48 and V50), which are shown to be brightened and reddened by nearby red giant stars. Also discovered among the previously known variable stars are three double-mode RR Lyrae stars (V8, V16, and V34) and several Blazhko variables. Archival Hubble Space Telescope images and the photometry by Johnson et al. (Cat. J/ApJ/527/199) have been used to define better the properties of the most crowded variable stars. The total number of cluster variable stars now stands at forty-seven: 23 RRab stars, four of which show Blazhko amplitude variations; 20 RRc stars, one showing clear Blazhko variations and another showing possible Blazhko variations; the three RRd stars, all having the dominant period ~0.36 day and period ratios P1/P0 ~0.7450; and an LPV star located near the tip of the red giant branch. A comparison of the RRd stars with those in other environments shows them to be most similar to those in IC4499.
- ID:
- ivo://CDS.VizieR/II/247
- Title:
- Variable Stars in the Large Magellanic Clouds
- Short Name:
- II/247
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The MACHO Project is a collaboration between scientists at the Mt. Stromlo & Siding Spring Observatories, the Center for Particle Astrophysics at the Santa Barbara, San Diego, & Berkeley campuses of the University of California, and the Lawrence Livermore National Laboratory. The primary aim of the project is a search for dark matter in the halo of the Milky Way in the form of objects like brown dwarfs or planets also named MACHOs, for MAssive Compact Halo Objects. The signature of these MACHOs is the occasional amplification of the light from extragalactic stars by the gravitational lens effect. The amplification can be large, but events are extremely rare: it is necessary to monitor photometrically several million stars for a period of years in order to obtain a useful detection rate. The MACHO project is described by Alcock et al. (1992, in "Robotic Telescopes in the 1990s", A.V. Fillippenko Ed., ASP Conf. Series 34, p.193). A dedicated 1.27-m telescope at Mount Stromlo, Australia is used to obtain observations of the LMC year-round, using a camera imaging a field of view of 0.5 square degrees at prime focus. Photometric observations of the LMC fields are obtained in two bandpasses simultaneously, using a dichroic beamsplitter to direct the blue (440-590nm) and red (590-780nm) light onto 2x2 mosaics of 2048x2048 Loral CCDs; the 15um pixels map to 0.63arcsec on the sky. The photometric reduction methods are detailed in Alcock et al. (1996ApJ...461...84A).
- ID:
- ivo://CDS.VizieR/J/AJ/108/932
- Title:
- Variable stars in the SMC cluster NGC 330
- Short Name:
- J/AJ/108/932
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- V and I band CCD images of the SMC cluster NGC 330 have been obtained over an interval of 4 years with the aim of identifying variable stars in and around this rich, young cluster. The search has revealed 22 Cepheid variables, of which 14 are newly discovered. All of these appear to belong to the SMC field population rather than being cluster members. Twenty long-period variables, and nine other variables were identified including two eclipsing variables (one newly discovered), and four close binary stars, two of which show emission lines. The Cepheids indicate that only small to moderate amounts of convective core overshoot (f_ov_<~0.25) occur during the main-sequence phases for stars of mass 2-3M_{sun}_. The Cepheid period-luminosity-color relation obtained from VI photometry, when compared to the theoretical relation of Chiosi, et al. (1993ApJS...86..541C), yields a distance modulus for the short-period Cepheids observed during this study of 18.92 if no overshoot is assumed, or 18.72 if moderate overshoot (f_ov=0.25) is adopted. Only two modes of pulsation are present in this group of Cepheids, most likely they are the fundamental and first overtone.
- ID:
- ivo://CDS.VizieR/J/MNRAS/480/669
- Title:
- Variable stars in the SMCNOD
- Short Name:
- J/MNRAS/480/669
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of a recently discovered stellar overdensity near the northern edge of the Small Magellanic Cloud (SMCNOD). We exploited variable stars from the fourth release of the Optical Gravitational Lensing Experiment. We used mainly pulsating variable stars and investigated their potential association with the SMCNOD using their spatial distribution and distances. We found four rather spatially concentrated anomalous Cepheids and eight evenly dispersed RR Lyrae stars to be most likely members of this overdensity. The anomalous Cepheids inside the SMCNOD trace possible intermediate-age population with ages ranging between 2 and 4.5Gyr. The age distribution of anomalous Cepheids seems to be in a good agreement with the age distribution of anomalous Cepheids in the SMC. Using empirical relations for RR Lyrae stars, we determined the median metallicity for a possible old population in the SMCNOD to be [Fe/H]_SMCNOD_=-1.71+/-0.21dex, which is in agreement with median metallicity of the old SMC population. The density profile for anomalous Cepheids shows a small anomaly at the position of the SMCNOD, on the other hand, RR Lyrae variables show no such deviation. The probability of finding the observed number of variable stars at the location of the SMCNOD by chance is very low for anomalous Cepheids (0.7 per cent) but high for RR Lyrae stars (13.0 per cent). Based on its variable stars content, we thus confirm the presence of a modest overdensity in intermediate-age stars in the SMCNOD and conclude that it probably has its origin in the SMC rather than to be the remnant of an accreted dwarf galaxy.
- ID:
- ivo://CDS.VizieR/J/MNRAS/339/701
- Title:
- Velocities and BR photometry in LMC
- Short Name:
- J/MNRAS/339/701
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a large spectroscopic survey of the LMC, consisting of more than 1300 radial velocities measured accurately with the 2dF instrument during three observing compaigns 1999-2002. In this sample, no evidence is found for any extraneous, kinematically distinct population over the expected LMC and Galactic components. We discuss the significance of this finding for the LMC self-lensing models. The sample was randomly selected from three APM photographic plates with 16<=R<=18mag and -1.0<=Bj-R<=2.5mag. The fields were centered on previous microlensing events. The 1200V grating was used with 1.1{AA} per pixel resolution over 4625-5765{AA}. The zero point of the velocity of LMC K-type stars is set by cross-correlating with a K-type standard star. For sample stars of other spectral type we assume no systematic change of the peak of velocity distribution with spectral type.
- ID:
- ivo://CDS.VizieR/J/A+A/462/683
- Title:
- Velocities in SMC field of NGC 330
- Short Name:
- J/A+A/462/683
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We search for the effects of metallicity on B and Be stars in the Small and Large Magellanic Clouds (SMC and LMC) and in the Milky Way (MW), by extending our previous analysis of B and Be star populations in the LMC to the SMC. The rotational velocities of massive stars and the evolutionary status of Be stars are examined with respect to their environments. Spectroscopic observations of hot stars belonging to the young cluster SMC-NGC 330 and its surrounding region were obtained with the VLT-GIRAFFE facilities in MEDUSA mode. We determined fundamental parameters for B and Be stars with the GIRFIT code, taking the effect of fast rotation and the age of observed clusters into account. We compared the mean vsini obtained by spectral type- and mass-selection for field and cluster B and Be stars in the SMC with the one in the LMC and MW.
- ID:
- ivo://CDS.VizieR/J/MNRAS/442/1663
- Title:
- Velocities of red giants in the SMC
- Short Name:
- J/MNRAS/442/1663
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from an extensive spectroscopic survey of field stars in the Small Magellanic Cloud (SMC). 3037 sources, predominantly first-ascent red giants, spread across roughly 37.5deg^2^, are analysed. The line-of-sight velocity field is dominated by the projection of the orbital motion of the SMC around the Large Magellanic Cloud/Milky Way. The residuals are inconsistent with both a non-rotating spheroid and a nearly face on disc system. The current sample and previous stellar and Hi kinematics can be reconciled by rotating disc models with line-of-nodes position angle {Theta} ~120{deg}-130{deg}, moderate inclination (25{deg}-70{deg}), and rotation curves rising at 20-40km/s/kpc. The metal-poor stars exhibit a lower velocity gradient and higher velocity dispersion than the metal-rich stars. If our interpretation of the velocity patterns as bulk rotation is appropriate, then some revision to simulations of the SMC orbit is required since these are generally tuned to the SMC disc line of nodes lying in a north-east-south-west (SW) direction. Residuals show strong spatial structure indicative of non-circular motions that increase in importance with increasing distance from the SMC centre. Kinematic substructure in the north-west part of our survey area is associated with the tidal tail or Counter-Bridge predicted by simulations. Lower line-of-sight velocities towards the Wing and the larger velocities just beyond the SW end of the SMC Bar are probably associated with stellar components of the Magellanic-Bridge and Counter-Bridge, respectively. Our results reinforce the notion that the intermediate-age stellar population of the SMC is subject to substantial stripping by external forces.
