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- ID:
- ivo://CDS.VizieR/J/AJ/157/22
- Title:
- Luminous and variable stars in NGC 2403 and M81
- Short Name:
- J/AJ/157/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of spectroscopy and multi-wavelength photometry of luminous and variable star candidates in the nearby spiral galaxies NGC 2403 and M81. We discuss specific classes of stars, the Luminous Blue Variables (LBVs), B[e] supergiants (sgB[e]), and the high-luminosity yellow hypergiants. We identify two new LBV candidates, and three sgB[e] stars in M81. We also find that some stars that were previously considered LBV candidates are actually field stars. The confirmed and candidate LBVs and sgB[e] stars together with the other confirmed members are shown on the HR Diagrams for their respective galaxies. We also present the HR Diagrams for the two "SN impostors", V37 (SN2002kg) and V12 (SN1954J) in NGC 2403 and the stars in their immediate environments.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A115
- Title:
- Luminous blue variables NACO and VISIR images
- Short Name:
- J/A+A/587/A115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Luminous blue variables (LBVs) are rare massive stars with very high luminosity. They are characterized by strong photometric and spectroscopic variability related to transient eruptions. The mechanisms at the origin of these eruptions is not well known. In addition, their formation is still problematic and the presence of a companion could help to explain how they form. This article presents a study of seven LBVs (about 20% of the known Galactic population), some Wolf-Rayet stars, and massive binaries. We probe the environments that surround these massive stars with near-, mid-, and far-infrared images, investigating potential nebula/shells and the companion stars. To investigate large spatial scales, we used seeing-limited and near diffraction-limited adaptive optics images to obtain a differential diagnostic on the presence of circumstellar matter and to determine their extent. From those images, we also looked for the presence of binary companions on a wide orbit. Once a companion was detected, its gravitational binding to the central star was tested. Tests include the chance projection probability, the proper motion estimates with multi-epoch observations, flux ratio, and star separations.
- ID:
- ivo://CDS.VizieR/J/ApJ/836/64
- Title:
- Luminous variable stars in M31 & M33. IV.
- Short Name:
- J/ApJ/836/64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this series of papers we have presented the results of a spectroscopic survey of luminous stars in the nearby spirals M31 and M33. Here, we present spectroscopy of 132 additional stars. Most have emission-line spectra, including luminous blue variables (LBVs) and candidate LBVs, Fe II emission line stars, the B[e] supergiants, and the warm hypergiants. Many of these objects are spectroscopically similar and are often confused with each other. We examine their similarities and differences and propose the following guidelines that can be used to help distinguish these stars in future work. (1) The B[e] supergiants have emission lines of [OI] and [FeII] in their spectra. Most of the spectroscopically confirmed sgB[e] stars also have warm circumstellar dust in their spectral energy distributions (SEDs). (2) Confirmed LBVs do not have the [OI] emission lines in their spectra. Some LBVs have [FeII] emission lines, but not all. Their SEDs show free-free emission in the near-infrared but no evidence for warm dust. Their most important and defining characteristic is the S Dor-type variability. (3) The warm hypergiants spectroscopically resemble the LBVs in their dense wind state and the B[e] supergiants. However, they are very dusty. Some have [FeII] and [OI] emission in their spectra like the sgB[e] stars, but are distinguished by their A- and F-type absorption-line spectra. In contrast, the B[e] supergiant spectra have strong continua and few if any apparent absorption lines. Candidate LBVs should share the spectral characteristics of the confirmed LBVs with low outflow velocities and the lack of warm circumstellar dust.
- ID:
- ivo://CDS.VizieR/J/ApJS/203/32
- Title:
- Machine-learned ASAS Classification Cat. (MACC)
- Short Name:
- J/ApJS/203/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Here, we describe a process to produce a probabilistic classification catalog of variability with machine learning from a multi-epoch photometric survey. In addition to producing accurate classifications, we show how to estimate calibrated class probabilities and motivate the importance of probability calibration. We also introduce a methodology for feature-based anomaly detection, which allows discovery of objects in the survey that do not fit within the predefined class taxonomy. Finally, we apply these methods to sources observed by the All-Sky Automated Survey (ASAS, Cat. II/264), and release the Machine-learned ASAS Classification Catalog (MACC), a 28 class probabilistic classification catalog of 50124 ASAS sources in the ASAS Catalog of Variable Stars. We estimate that MACC achieves a sub-20% classification error rate and demonstrate that the class posterior probabilities are reasonably calibrated. MACC classifications compare favorably to the classifications of several previous domain-specific ASAS papers and to the ASAS Catalog of Variable Stars, which had classified only 24% of those sources into one of 12 science classes.
- ID:
- ivo://CDS.VizieR/J/ApJ/631/906
- Title:
- MACHO Galactic Bulge microlensing events
- Short Name:
- J/ApJ/631/906
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 450 relatively high signal-to-noise ratio microlensing events observed by the MACHO collaboration between 1993 and 1999. The events are distributed throughout our fields, and as expected, they show a clear concentration toward the Galactic center. No optical depth is given for this sample, since no blending efficiency calculation has been performed and we find evidence for substantial blending. In a companion paper we give optical depths for the subsample of events on clump giant source stars, where blending is a less significant effect. Several events with sources that may belong to the Sagittarius dwarf galaxy are identified. For these events even relatively low dispersion spectra could suffice to classify these events as either consistent with Sagittarius membership or as non-Sagittarius sources. Several unusual events, such as microlensing of periodic variable source stars, binary lens events, and an event showing extended source effects, are identified. We also identify a number of contaminating background events as cataclysmic variable stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/542/257
- Title:
- MACHO LMC first-overtone RR Lyrae
- Short Name:
- J/ApJ/542/257
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- More than 1300 variables classified provisionally as first-overtone RR Lyrae pulsators in the MACHO variable-star database of the Large Magellanic Cloud (LMC) have been subjected to standard frequency analysis. Based on the remnant power in the prewhitened spectra, we found 70% of the total population to be monoperiodic. The remaining 30% (411 stars) are classified as one of nine types according to their frequency spectra. Several types of RR Lyrae pulsational behavior are clearly identified here for the first time. Together with the earlier discovered double-mode (fundamental and first-overtone) variables, this study increased the number of known double-mode stars in the LMC to 181. During the total 6.5yr time span of the data, 10% of the stars showed strong period changes.
- ID:
- ivo://CDS.VizieR/J/AJ/135/83
- Title:
- MACHO LMC first overtone RR Lyrae
- Short Name:
- J/AJ/135/83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Previous studies have indicated that many of the RR Lyrae variables in the LMC have properties similar to those in the Galactic globular cluster M3. Assuming that the M3 RR Lyrae variables follow the same relationships among period, temperature, amplitude, and Fourier phase parameter phi31 as their LMC counterparts, we have used the M3 phi31-logP relation to identify the M3-like unevolved first overtone RR Lyrae variables in 16 MACHO fields near the LMC bar.
- ID:
- ivo://CDS.VizieR/J/AJ/127/334
- Title:
- MACHO LMC first-overtone RR Lyrae variables
- Short Name:
- J/AJ/127/334
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Shapes of RR Lyrae light curves can be described in terms of Fourier coefficients that past research has linked with physical characteristics such as luminosity, mass, and temperature. Fourier coefficients have been derived for the V and R light curves of 785 overtone RR Lyrae variables in 16 MACHO fields near the bar of the LMC.
- ID:
- ivo://CDS.VizieR/J/AJ/115/1894
- Title:
- M31A eclipsing binaries and Cepheids
- Short Name:
- J/AJ/115/1894
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have undertaken a long-term project, DIRECT, to obtain the direct distances to two important galaxies in the cosmological distance ladder, M31 and M33, using detached eclipsing binaries (DEBs) and Cepheids. While rare and difficult to detect, DEBs provide us with the potential to determine these distances with an accuracy better than 5%. The extensive photometry obtained in order to detect DEBs provides us with good light curves for the Cepheid variables. These are essential to the parallel project to derive direct Baade-Wesselink distances to Cepheids in M31 and M33. For both Cepheids and eclipsing binaries, the distance estimates will be free of any intermediate steps. As a first step in the DIRECT project, between 1996 September and 1997 January we obtained 36 full nights on the Michigan-Dartmouth-MIT Observatory 1.3m telescope and 45 full/partial nights on the F. L. Whipple Observatory 1.2m telescope to search for DEBs and new Cepheids in the M31 and M33 galaxies. In this paper, second in a series, we present the catalog of variable stars, most of them newly detected, found in the field M31A [({alpha},{delta})=(11.34{deg}, 41.73{deg}), J2000.0]. We have found 75 variable stars: 15 eclipsing binaries, 43 Cepheids, and 17 other periodic, possible long-period or nonperiodic variables. The catalog of variables, as well as their photometry and finding charts, is available via anonymous ftp and the World Wide Web. The CCD frames are available upon request.
