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541. I-band light curves of OGLE LMC Miras
ID:
ivo://CDS.VizieR/J/AJ/152/164
Title:
I-band light curves of OGLE LMC Miras
Short Name:
J/AJ/152/164
Date:
21 Oct 2021
Publisher:
CDS
Description:
We develop a nonlinear semi-parametric Gaussian process model to estimate periods of Miras with sparsely sampled light curves. The model uses a sinusoidal basis for the periodic variation and a Gaussian process for the stochastic changes. We use maximum likelihood to estimate the period and the parameters of the Gaussian process, while integrating out the effects of other nuisance parameters in the model with respect to a suitable prior distribution obtained from earlier studies. Since the likelihood is highly multimodal for period, we implement a hybrid method that applies the quasi-Newton algorithm for Gaussian process parameters and search the period/frequency parameter space over a dense grid. A large-scale, high-fidelity simulation is conducted to mimic the sampling quality of Mira light curves obtained by the M33 Synoptic Stellar Survey. The simulated data set is publicly available and can serve as a testbed for future evaluation of different period estimation methods. The semi-parametric model outperforms an existing algorithm on this simulated test data set as measured by period recovery rate and quality of the resulting period-luminosity relations.
542. Identification and coordinates in M4
ID:
ivo://CDS.VizieR/J/PAZh/22/847
Title:
Identification and coordinates in M4
Short Name:
J/PAZh/22/847
Date:
21 Oct 2021
Publisher:
CDS
Description:
Accurate equatorial coordinates have been determined for 54 variable stars in the globular cluster M 4=NGC 6121.
543. Identification and coordinates in M 53
ID:
ivo://CDS.VizieR/J/PAZh/23/454
Title:
Identification and coordinates in M 53
Short Name:
J/PAZh/23/454
Date:
21 Oct 2021
Publisher:
CDS
Description:
Equatorial coordinates have been determined for 61 variables in the northern globular cluster M 53 and for 12 variables in the southern globular cluster NGC 2808 with accuracy sufficient for reliable identifications. A number of errors have been revealed in publications on variable starts in M 53.
544. Identification of Dahlmark variables
ID:
ivo://CDS.VizieR/IV/29
Title:
Identification of Dahlmark variables
Short Name:
IV/29
Date:
21 Oct 2021
Publisher:
CDS
Description:
The amateur observer Lennart Dahlmark has published a useful series of IBVS notes listing a number of candidate variable stars, most of which were new. Although adequate charts and reliable semi-accurate positions were supplied, no other identifications were usually given. If the stars are to be recovered for further study and linkage within other surveys (IRAS, etc.), then precise positions must be determined to make identification unambiguous within crowded galactic fields.
545. Identification of RR Lyrae stars from the DES
ID:
ivo://CDS.VizieR/J/AJ/158/16
Title:
Identification of RR Lyrae stars from the DES
Short Name:
J/AJ/158/16
Date:
21 Oct 2021
Publisher:
CDS
Description:
Many studies have shown that RR Lyrae variable stars (RRL) are powerful stellar tracers of Galactic halo structure and satellite galaxies. The Dark Energy Survey (DES), with its deep and wide coverage (g~23.5 mag in a single exposure; over 5000 deg^2^) provides a rich opportunity to search for substructures out to the edge of the Milky Way halo. However, the sparse and unevenly sampled multiband light curves from the DES wide-field survey (a median of four observations in each of grizY over the first three years) pose a challenge for traditional techniques used to detect RRL. We present an empirically motivated and computationally efficient template-fitting method to identify these variable stars using three years of DES data. When tested on DES light curves of previously classified objects in SDSS stripe 82, our algorithm recovers 89% of RRL periods to within 1% of their true value with 85% purity and 76% completeness. Using this method, we identify 5783 RRL candidates, ~28% of which are previously undiscovered. This method will be useful for identifying RRL in other sparse multiband data sets.
546. Identifications of Sonneberg variables
ID:
ivo://CDS.VizieR/IV/23
Title:
Identifications of Sonneberg variables
Short Name:
IV/23
Date:
21 Oct 2021
Publisher:
CDS
Description:
The list below is a continuation of a series providing accurate positions and identifications for variables appearing on the MVS charts (Hoffmeister, 1957, Mitt. Verdander. Sterne, No. 245). The variables here were first described by Hoffmeister (1949, Astron. Abh. Ergaenzungshefte z.d. Astron. Nach., 12, no. 1, A3) in the difficult-to-find ``Ergaenzungshefte'' to the Astronomische Nachrichten, and are the first group from a collection of some 1440 variables from this publication. Details about the identification procedure and table layout are contained in the first report of our series (Kinnunen & Skiff, 2000IBVS.4862....1K). We are grateful to librarians Antoinette Beiser (Lowell) and Brenda Corbin (U. S. Naval Observatory, Washington) for providing a photocopy of the Hoffmeister survey; ``bibliothecaire extraordinaire'' Suzanne Laloe (Obs. Paris-Meudon) advised on how this obscure journal should be cited.
547. II Pegasi spectra with PEPSI
ID:
ivo://CDS.VizieR/J/A+A/625/A27
Title:
II Pegasi spectra with PEPSI
Short Name:
J/A+A/625/A27
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a temperature and a magnetic-field surface map of the K2 subgiant of the active binary II Peg. Employed are high resolution Stokes IV spectra obtained with the new Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT). Fourteen average line profiles are inverted using our iMap code. We have employed an iterative regularization scheme without the need of a penalty function and incorporate a physical 3D description of the surface field vector. The spectral resolution of our data is 130000 which converts to 20 resolution elements across the disk of II Peg. Our main result is that the temperature features on II Peg closely correlate with its magnetic field topology. We find a warm spot (350K warmer with respect to the effective temperature) of positive polarity and radial field density of 1.1kG coexisting with a cool spot (780K cooler) of negative polarity of 2kG. Several other cool features are reconstructed containing both polarities and with (radial) field densities of up to 2kG. The largest cool spot is reconstructed with a temperature contrast of 550K, an area of almost 10% of the visible hemisphere, and with a multipolar magnetic morphology. A meridional and an azimuthal component of the field of up to +/-500G is detected in two surface regions between spots with strong radial fields but different polarities. A force-free magnetic-field extrapolation suggests that the different polarities of cool spots and the positive polarity of warm spots are physically related through a system of coronal loops of typical height of ~=2R*. While the H{alpha} line core and its red-side wing exhibit variations throughout all rotational phases, a major increase of blue-shifted H{alpha} emission was seen for the phases when the warm spot is approaching the stellar central meridian indicating high-velocity mass motion within its loop. Active stars such as II Peg can show coexisting cool and warm spots on the surface that we interpret resulting from two different formation mechanisms. We explain the warm spots due to photospheric heating by a shock front from a siphon-type flow between regions of different polarities while the majority of the cool spots is likely formed due to the expected convective suppression like on the Sun.
548. II Pegasus photometry during 1979-2010
ID:
ivo://CDS.VizieR/J/A+A/559/A97
Title:
II Pegasus photometry during 1979-2010
Short Name:
J/A+A/559/A97
Date:
21 Oct 2021
Publisher:
CDS
Description:
According to earlier Doppler images of the magnetically active primary giant component of the RS CVn binary II Peg, the surface of the star was dominated by one single active longitude that was clearly drifting in the rotational frame of the binary system during 1994-2002; later imaging for 2004-2010, however, showed decreased and chaotic spot activity, with no signs of the drift pattern. Here we set out to investigate from a more extensive photometric dataset whether such a drift is a persistent phenomenon, in which case it could be due to either an azimuthal dynamo wave or an indication of the binary system orbital synchronization still being incomplete. We analyse the datasets using the Carrier Fit method (hereafter CF), especially suitable for analyzing time series in which a fast clocking frequency (such as the rotation of the star) is modulated with a slower process (such as the stellar activity cycle).
549. IJKs photometry of Galactic bulge variables
ID:
ivo://CDS.VizieR/J/A+A/362/215
Title:
IJKs photometry of Galactic bulge variables
Short Name:
J/A+A/362/215
Date:
21 Oct 2021
Publisher:
CDS
Description:
Repeated DENIS observations (summer 1996 & 1998) in the J (1.25{mu}m) and the K_s_ (2.15{mu}m) bands are used to look for variables stars. We present two catalogues of ~1000 probable variables in an area of ~4deg^2^ of the inner galactic bulge. The first one contains ~720 variable star candidates which which show variability in the J and K_s_ while the second consists of sources only observed to be variable in K_s_ (~270 sources), mainly in regions whit high interstellar extinction.
550. I light curves of RR Lyrae from OGLE II
ID:
ivo://CDS.VizieR/J/other/PZP/9.5
Title:
I light curves of RR Lyrae from OGLE II
Short Name:
J/other/PZP/9.5
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the discovery of ten RR Lyrae variables. They were found in a search for new variables in the OGLE II Photometric Database (Szymanski 2005AcA....55...43S, Udalski et al. 1997AcA....47..319U). Suitable parameters (e.g. Isig>0.1, e_Imed<Isig) were used in the OGLE Photometry Database Query Page (http://ogledb.astrouw.edu.pl/~ogle/photdb/) for stars in the Galactic Disk. Period analysis was made with the software AVE (GEA).