- ID:
- ivo://CDS.VizieR/J/A+A/628/A51
- Title:
- Magellanic Clouds reddening map
- Short Name:
- J/A+A/628/A51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The reddening maps of the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) are constructed using the Cepheid period-luminosity (P-L) relations. We examine reddening distribution across the LMC and SMC through large data sets on classical Cepheids provided by the OGLE Phase IV survey. We also investigate the age and spatio-temporal distributions of Cepheids to understand the recent star formation history in the LMC and SMC. The V and I band photometric data of 2476 fundamental mode (FU) and 1775 first overtone mode (FO) Cepheids in the LMC, and 2753 FU and 1793 FO Cepheids in the SMC were analysed for their P-L relations. We converted the period of FO Cepheids to the corresponding period of FU Cepheids before combining the two modes of Cepheids. Both galaxies were divided into small segments and combined FU and FO P-L diagrams were drawn in two bands for each segment. The reddening analysis was performed on 133 segments covering a total area of about 154.6deg^2^ in the LMC and 136 segments covering a total area of about 31.3deg^2^ in the SMC. By comparison with well-calibrated P-L relations of these two galaxies, we determined reddening E(V-I) in each segment and equivalent reddening E(B-V) assuming the normal extinction law. The period-age relations were used to derive the age of the Cepheids. Reddening maps were constructed using reddening values in different segments across the LMC and SMC. We find clumpy structures in the reddening distributions of the LMC and SMC. From the reddening map of the LMC, highest reddening of E(V-I)=0.466mag is traced in the region centred at RA~85.13deg, DEC~-69.34deg which is in close vicinity of the star forming HII region 30 Doradus. In the SMC, maximum reddening of E(V-I)=0.189mag is detected in the region centred at RA~12.10deg, DEC~-73.07deg. The mean reddening values in the LMC and SMC are estimated as E(V-I)_LMC_=0.113+/-0.060mag, E(B-V)_LMC_=0.091+/-0.050mag, E(V-I)_SMC_=0.049+/-0.070mag, and E(B-V)_SMC_=0.038+/-0.053mag. The LMC reddening map displays heterogeneous distribution having small reddening in the central region and higher reddening towards the eastern side of the LMC bar. The SMC has relatively small reddening in its peripheral regions but larger reddening towards the south-west region. In these galaxies, we see evidence of a common enhanced Cepheid population at around 200 Myr ago which appears to have occurred due to a close encounter between the two clouds.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/159/114
- Title:
- Magnetic CVs spectra & other variable objects II.
- Short Name:
- J/AJ/159/114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the second paper of a series presenting our search for magnetic cataclysmic variables (mCVs) among candidates selected mostly from the Catalina Real-Time Transient Survey. We present the identification spectra, obtained at the SOAR Telescope, as well as magnitudes and Gaia distances for 45 objects. Of these, 39 objects are identified as CVs, from which 8 targets show observational characteristics of mCVs, being 7 polars and 1 intermediate polar. The remaining 31 CVs in our sample are probably non-magnetic systems, in low (22 systems) or high (9 systems) accretion states. Six targets of the sample are not CVs (5 active galactic nuclei and 1 T-Tauri star). Among the 8 objects with mCV spectra, 6 are new classifications. Three polars were observed in low-accretion state, either revealing photospheric features of the secondary star and allowing the estimation of their spectral type, or presenting H{beta} Zeeman components associated to the white dwarf (WD) magnetic field. In addition to the results obtained in the first paper of the series, and depending on the confirmation of these classifications by observational follow-up, our results would increase the sample of known polars by about 9%.
- ID:
- ivo://CDS.VizieR/J/A+A/411/565
- Title:
- Magnetic field in V2052 Oph
- Short Name:
- J/A+A/411/565
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- V2052 Oph is a {beta} Cep star with vsini~60km/s. The behavior of its stellar wind was studied in the ultraviolet wavelength region with the IUE satellite. It revealed periodic variations in the equivalent widths (EW) of the resonance lines of wind-sensitive ions with a period of 3.638833d, which is identified as the rotational period. These variations are typical of magnetic stars. Therefore time-resolved circular spectropolarimetric observations were obtained with the Musicos echelle spectropolarimeter at the 2-m Telescope Bernard Lyot (TBL) to search for a magnetic field in the star. Stokes V patterns were observed, the inclination and magnetic angles were derived and a value was determined for the polar magnetic field (250+/-190G) using an oblique rotator dipole model. The spectroscopic information was used to search for periodicity in line-profile variations (lpv), radial velocity and minimum intensity curves. Multiperiodicity was found, corresponding to radial (f1=7.15c/d) and non-radial (f2=6.82c/d, l=3 or 4) pulsation modes. The rotation period is also detected in rotationally modulated observables because of the magnetic poles passing through the observer's line of sight. We determined the stellar parameters of the star, which was found to be chemically peculiar, in particular He-enriched. This makes V2052 Oph the first magnetic He-strong early B star with known pulsational properties.
- ID:
- ivo://CDS.VizieR/J/AJ/119/1760
- Title:
- M54 and Sgr dSph VI photometry
- Short Name:
- J/AJ/119/1760
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present deep VI-band photometry of the globular cluster M54, a nearby field in the Sagittarius dwarf galaxy, and a control field. The color-magnitude diagrams reach well below the oldest main-sequence turnoffs, thus enabling an analysis of the galaxy's age-metallicity relation with unprecedented clarity. We also study the variable stars in the direction of M54. From 67 RR Lyrae variables, we confirm and improve on our previous estimates of the cluster horizontal branch magnitude, foreground reddening, and horizontal branch morphology. These values are used in determining the ages of M54 and the Sagittarius field populations. We confirm our previous result that M54 is the same age as Galactic globular clusters of similar metallicity.
- ID:
- ivo://CDS.VizieR/J/other/IBVS/4431
- Title:
- Margoni-Stagni variables
- Short Name:
- J/other/IBVS/443
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In a 1984 publication, "A search for new variable stars in the Milky Way field at l=780{deg}, b=-60{deg}", R. Margoni and R. Stagni give finding charts, light curves, and elements for 99 new variable stars. A follow-up paper (Margoni et al., 1989A&AS...81..393M) contains additional observations for the same stars. About three-quarters of these are now named variables. I have gone through this list to determine precise positions for all the stars, and have made identifications with the IRAS and GSC catalogues.
- ID:
- ivo://CDS.VizieR/J/A+A/617/A32
- Title:
- MASCARA bright variable stars light curves
- Short Name:
- J/A+A/617/A32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Multi-site All-Sky CAmeRA (MASCARA) aims to find the brightest transiting planet systems by monitoring the full sky at magnitudes 4<V<8.4, taking data every 6.4 seconds. The northern station has been operational on La Palma since February 2015. These data can also be used for other scientific purposes, such as the study of variable stars. In this paper we aim to assess the value of MASCARA data for studying variable stars by determining to what extent known variable stars can be recovered and characterised, and how well new, unknown variables can be discovered. We used the first 14 months of MASCARA data, consisting of the light curves of 53401 stars with up to one million flux points per object. All stars were cross-matched with the VSX catalogue to identify known variables. The MASCARA light curves were searched for periodic flux variability using generalised Lomb-Scargle periodograms. If significant variability of a known variable was detected, the found period and amplitude were compared with those listed in the VSX database. If no previous record of variability was found, the data were phase folded to attempt a classification. Of the 1919 known variable stars in the MASCARA sample with periods 0.1<P<10-days, amplitudes >2%, and that have more than 80 hours of data, 93.5% are recovered. In addition, the periods of 210 stars without a previous VSX record were determined, and 282 candidate variable stars were newly identified. We also investigated whether second order variability effects could be identified. The O'Connell effect is seen in seven eclipsing binaries, of which two have no previous record of this effect. MASCARA data are very well suited to study known variable stars. They also serve as a powerful means to find new variables among the brightest stars in the sky. Follow-up is required to ensure that the observed variability does not originate from faint background objects.
- ID:
- ivo://CDS.VizieR/J/ApJS/203/33
- Title:
- 2MASS interferometric calibrator candidates
- Short Name:
- J/ApJS/203/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to provide a list of sources found to be unresolved from direct observations with high angular resolution and dynamic range, which can be used to choose interferometric calibrators. To this purpose, we have used a large number of lunar occultations recorded with the ISAAC instrument at the Very Large Telescope to select sources found to be unresolved and without close companions. An algorithm has been used to determine the limiting angular resolution achieved for each source, taking into account a noise model built from occulted and unocculted portions of the light curves. We have obtained upper limits on the angular sizes of 556 sources, with magnitudes ranging from Ks~4 to 10, with a median of 7.2mag. The upper limits on possible undetected companions (within ~0.5") range from Ks~8 to 13, with a median of 11.5mag. One-third of the sources have angular sizes <=1mas, and two-thirds have sizes <=2mas. This list of unresolved sources matches well the capabilities of current large interferometric facilities. We also provide available cross-identifications, magnitudes, spectral types, and other auxiliary information. A fraction of the sources are found to be potentially variable. The list covers parts of the Galactic Bulge and in particular the vicinity of the Galactic Center, where extinction is very significant and traditional lists of calibrators are often insufficient.
- ID:
- ivo://CDS.VizieR/J/ApJ/748/96
- Title:
- Massive binaries in the LMC
- Short Name:
- J/ApJ/748/96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The stellar mass-luminosity relation is poorly constrained by observations for high-mass stars. We describe our program to find eclipsing massive binaries in the Magellanic Clouds using photometry of regions rich in massive stars, and our spectroscopic follow-up to obtain radial velocities and orbits. Our photometric campaign identified 48 early-type periodic variables, of which only 15 (31%) were found as part of the microlensing surveys. Spectroscopy is now complete for 17 of these systems, and in this paper we present analysis of the first two, LMC 172231 and ST2-28, simple detached systems of late-type O dwarfs of relatively modest masses. Our orbit analysis yields very precise masses (~2%), and we use tomography to separate the components and determine effective temperatures by model fitting, necessary for determining accurate (0.05-0.07 dex) bolometric luminosities in combination with the light-curve analysis. Our approach allows more precise comparisons with evolutionary theory than previously possible. To our considerable surprise, we find a small, but significant, systematic discrepancy: all of the stars are slightly undermassive, by typically 11% (or overluminous by 0.2 dex) compared with that predicted by the evolutionary models. We examine our approach for systematic problems, but find no satisfactory explanation. The discrepancy is in the same sense as the long-discussed and elusive discrepancy between the masses measured from stellar atmosphere analysis with the stellar evolutionary models, and might suggest that either increased rotation or convective overshooting is needed in the models.
- ID:
- ivo://CDS.VizieR/J/AJ/138/1508
- Title:
- 2MASS large-amplitude variable stars
- Short Name:
- J/AJ/138/1508
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of variable stars in the near-infrared wavelength detected with overlapping regions of the Two Micron All Sky Survey public images, and discuss their properties. The investigated region is in the direction of the Galactic center (-30{deg}<~l<~20, |b|<~20), which covers the entire bulge. We have detected 136 variable stars, of which six are already known and 118 are distributed in the |b|<5{deg} region. Additionally, 84 variable stars have optical counterparts in Digitized Sky Survey images. The three diagrams (color-magnitude, light variance, and color-color diagrams) indicate that most of the detected variable stars should be large-amplitude and long-period variables such as Mira variables or OH/IR stars. The number density distribution of the detected variable stars implies that they trace the bar structure of the Galactic bulge.
- ID:
- ivo://CDS.VizieR/J/A+A/622/A120
- Title:
- Mass loss from Miras with and without Tc
- Short Name:
- J/A+A/622/A120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We follow-up on a previous finding that AGB Mira variables containing the third dredge-up indicator technetium (Tc) in their atmosphere form a different sequence of K-[22] colour as a function of pulsation period than Miras without Tc. A near- to mid-infrared colour such as K-[22] is a good probe for the dust mass-loss rate of the stars. Contrary to what might be expected, Tc-poor Miras show redder K-[22] colours (i.e. higher dust mass-loss rates) than Tc-rich Miras at a given period. Here, the previous sample is extended and the analysis is expanded towards other colours and dust spectra. The most important aim is to investigate if the same two sequences can be revealed in the gas mass-loss rate. We analysed new optical spectra and expanded the sample by including more stars from the literature. Near- and mid-IR photometry and ISO dust spectra of our stars were investigated where available. Literature data of gas mass-loss rates of Miras and semi-regular variables were collected and analysed. Our results show that Tc-poor Miras are redder than Tc-rich Miras in a broad range of the mid-IR, suggesting that the previous finding based on the K-[22] colour is not due to a specific dust feature in the 22-micron band. We establish a linear relation between K-[22] and the gas mass-loss rate. We also find that the 13 micron feature disappears above K-[22]~2.17mag, corresponding to dM/dt}_g_~2.6x10^-7^M_{sun}/yr. No similar sequences of Tc-poor and Tc-rich Miras in the gas mass-loss rate vs. period diagram are found, most probably owing to limitations in the available data. Different hypotheses to explain the observation of two sequences in the P vs. K-[22] diagram are discussed and tested, but so far, none of them convincingly explains the observations. Nevertheless, we might have found an hitherto unknown but potentially important process influencing mass loss on the TP-AGB.
