- ID:
- ivo://CDS.VizieR/J/ApJS/191/389
- Title:
- Photometric monitoring in {sigma} Ori cluster
- Short Name:
- J/ApJS/191/389
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-precision photometry on 107 variable low-mass stars and brown dwarfs in the ~3Myr {sigma} Orionis open cluster. We have carried out I-band photometric monitoring within two fields, encompassing 153 confirmed or candidate members of the low-mass cluster population, from 0.02 to 0.5M_{sun}_. We are sensitive to brightness changes on timescales from 10 minutes to two weeks with amplitudes as low as 0.004mag, and find variability on these timescales in nearly 70% of cluster members. We identify both periodic and aperiodic modes of variability, as well as semi-periodic rapid fading events that are not accounted for by the standard explanations of rotational modulation of surface features or accretion. We have incorporated both optical and infrared color data to uncover trends in variability with mass and circumstellar disks.
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- ID:
- ivo://CDS.VizieR/J/A+A/568/A100
- Title:
- Photometric monitoring of halo C stars
- Short Name:
- J/A+A/568/A100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Carbon stars are among the brightest intermediate-age stars. They are seen in nearly all galaxies of the Local Group. In the Milky Way they are members of the thin disk but over a hundred have been identified in the Galactic halo. Since the halo consists essentially of an old stellar population, these carbon stars warrant special attention. We believe that such stars are trespassers and belong to streams left over by disrupted dwarf spheroidal galaxies. By performing photometric monitoring we intend to identify Miras among the halo carbon stars. We obtained, over several semesters, K and J images centered on the carbon stars in order to determine their variation and periodicity.
- ID:
- ivo://CDS.VizieR/J/AJ/158/180
- Title:
- Photometric observations of AE Cassiopeia
- Short Name:
- J/AJ/158/180
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- AE Cas was observed some 40 yr ago by Srivastava & Kandpal (1984AcA....34..281S) and was analyzed by Kopal's Fourier frequency-domain technique. No further precision observations have taken place until the present study, which represents the first modern synthetic analysis of light curves using the 2016 version of the Wilson-Devinney (W-D) Program. It was observed in 2015 October 2, 3 and 23, inclusive, at Dark Sky Observatory in North Carolina with the 0.81 m reflector of Appalachian State University and the 0.9 m reflector at Kitt Peak National Observatory remotely through the Southeastern Association for Research in Astronomy (SARA) consortia. V, R_c_, I_c_ observations were taken. Five times of minimum light were determined from our present observations, which include three primary eclipses and two secondary eclipses. In addition, eight observations at minima were introduced as low weighted times of minimum light from archived All-Sky Automated Survey for Supernovae Variable Star Catalog (ASAS) data and 74 times of minimum light from the literature, some of which were from visual observations. This period study covers an interval of some 89 yr. The period was found to be decaying at a constant rate with a high level of confidence. A VR_c_I_c_ simultaneous W-D Program solution indicates that the system has a mass ratio somewhat less than unity (q=0.856+/-0.001), and a component temperature difference of ~2060 K. A q-search was performed and the mass ratio minimized at the above value. The large temperature difference in the components verifies that the binary is not yet in contact. No spots were needed for the solution. The fill-out of our model is 83.2% for the primary component (smaller radius) and 99.1% for the secondary component. So, it is near a classical Algol configuration.
- ID:
- ivo://CDS.VizieR/J/AJ/156/227
- Title:
- Photometric observations of the K2-22 system
- Short Name:
- J/AJ/156/227
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 45 ground-based photometric observations of the K2-22 system collected between 2016 December and 2017 May, which we use to investigate the evolution of the transit of the disintegrating planet K2-22b. Last observed in early 2015, in these new observations we recover the transit at multiple epochs and measure a typical depth of <1.5%. We find that the distribution of our measured transit depths is comparable to the range of depths measured in observations from 2014 and 2015. These new observations also support ongoing variability in the K2-22b transit shape and time, although the overall shallowness of the transit makes a detailed analysis of these transit parameters difficult. We find no strong evidence of wavelength-dependent transit depths for epochs where we have simultaneous coverage at multiple wavelengths, although our stacked Las Cumbres Observatory data collected over days-to-months timescales are suggestive of a deeper transit at blue wavelengths. We encourage continued high-precision photometric and spectroscopic monitoring of this system in order to further constrain the evolution timescale and to aid comparative studies with the other few known disintegrating planets.
- ID:
- ivo://CDS.VizieR/J/AJ/138/1435
- Title:
- Photometric observations of UX Monocerotis
- Short Name:
- J/AJ/138/1435
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze eight years (1999-2007) of automated photometric observations of the active Algol binary UX Monocerotis (HD 65607; P=5.90day; A5III-IVe+G2III) to search for mass transfer bursts similar to those seen in U Cephei. The largest photometric anomaly is the mean gainer luminosity difference between the stream-impact hemisphere and the opposite hemisphere. We find an updated Wilson-Devinney solution for earlier six-color observations. The UX Mon donor star fills its Roche lobe and the gainer nearly fills its rotational lobe. Instead of isolated bursts of the U Cep type, we found nearly continuous brightness fluctuations likely produced by variable mass transfer.
- ID:
- ivo://CDS.VizieR/J/ApJ/702/403
- Title:
- Photometric observations of V1197 Orionis
- Short Name:
- J/ApJ/702/403
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- V1197 Orionis light curves from a long-term observing program for red giant binaries show ellipsoidal variation of small amplitude in the V and R_C_ bands, although not clearly in U and B. Eclipses are not detected. All four bands show large irregular intrinsic variations, including fleeting quasi-periodicities identified by power spectra, that degrade analysis and may be caused by dynamical tides generated by orbital eccentricity. To deal with the absence of eclipses and consequent lack of astrophysical and geometrical information, direct use is made of the Hipparcos parallax distance while the V and R_C_ light curves and (older) radial velocity curves are analyzed simultaneously in terms of absolute flux. The red giant's temperature is estimated from new spectra. The dim companion has not been observed or discussed in the literature but most solutions find its mass to be well below that of the red giant. Solutions show red giant masses that are too low for evolution to the red giant stage within the age of the Galaxy, although that result is probably an artifact of the intrinsic brightness fluctuations.
- ID:
- ivo://CDS.VizieR/J/AJ/158/175
- Title:
- Photometric & spectroscopic study of AF And in M31
- Short Name:
- J/AJ/158/175
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a photometric and spectroscopic analysis of the Hubble-Sandage variable star AF And in M31. The data have been taken under the Nainital Microlensing Survey during 1998-2002, and follow-up observations were carried out until 2011. During this period, photometric observations in Cousins R and I bands were obtained for 169 nights spanning about 5000 days. AF And showed a prominent outburst around 1999 mid-January, followed by a gradual decrease in brightness of about 1.5 mag in the next 3 yr with a declining rate of ~0.0015 mag/day, leading to a quiescent phase at the end of 2001. After lying low for about 9 yr, AF And again went through a secondary outburst phase in late 2010 with an amplitude of 0.44 mag, where it lasted for one year before fading back to its quiescent phase. Spectroscopic observations of AF And show prominent Balmer and He I emission lines along with the comparatively weaker Fe II and [Fe II] emissions. Asymmetric emission line profiles in its spectrum imply a mass-loss rate of about 2.2x10^-4^ M_{sun}_/yr through the stellar winds in the photosphere. Using spectral energy distribution fitting, we find a photospheric temperature of 33000+/-3000 K during the visual minimum. Using a weak P Cygni profile of the He I emission line, the wind terminal velocity for AF And is found to be around 280-300 km/s.
- ID:
- ivo://CDS.VizieR/J/AJ/152/75
- Title:
- Photometric survey of IC 2391, {eta} Cha, and USco
- Short Name:
- J/AJ/152/75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The past two decades have seen a significant advancement in the detection, classification, and understanding of exoplanets and binaries. This is due, in large part, to the increase in use of small-aperture telescopes (<20cm) to survey large areas of the sky to milli-mag precision with rapid cadence. The vast majority of the planetary and binary systems studied to date consists of main-sequence or evolved objects, leading to a dearth of knowledge of properties at early times (<50Myr). Only a dozen binaries and one candidate transiting Hot Jupiter are known among pre-main-sequence objects, yet these are the systems that can provide the best constraints on stellar formation and planetary migration models. The deficiency in the number of well characterized systems is driven by the inherent and aperiodic variability found in pre-main-sequence objects, which can mask and mimic eclipse signals. Hence, a dramatic increase in the number of young systems with high-quality observations is highly desirable to guide further theoretical developments. We have recently completed a photometric survey of three nearby (<150pc) and young (<50Myr) moving groups with a small-aperture telescope. While our survey reached the requisite photometric precision, the temporal coverage was insufficient to detect Hot Jupiters. Nevertheless, we discovered 346 pre-main-sequence binary candidates, including 74 high-priority objects for further study.
- ID:
- ivo://CDS.VizieR/J/A+A/581/A138
- Title:
- Photometric variability in magnetic CP stars
- Short Name:
- J/A+A/581/A138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The (magnetic) chemically peculiar (CP) stars of the upper main sequence are well-suited laboratories for investigating the influence of magnetic fields on the stellar surface because they produce abundance inhomogeneities (spots), which results in photometric variability that is explained in terms of the oblique rotator model. CP stars exhibiting this phenomenon are normally classified as {alpha}^2^ Canum Venaticorum (ACV) variables. It is important to increase the sample of known rotational periods among CP stars by discovering new ACV variables. An increased sample size will contribute to the understanding of the CP stars' evolution in time. We aim at discovering new ACV variables in the public data of the third phase of the All Sky Automated Survey (ASAS-3). Furthermore, by analysis of the available photometric data, we intend to derive rotational periods of the stars. The ASAS-3 data were cross-correlated with the Catalogue of Ap, HgMn, and Am stars in order to analyse the light curves of bona fide CP and related stars. The light curves were downloaded and cleaned of outliers and data points with a flag indicating bad quality. Promising candidates showing a larger scatter than observed for constant stars in the corresponding magnitude range were searched for periodic signals using a standard Fourier technique. Objects exhibiting periodic signals well above the noise level were considered and visually inspected, whereas borderline cases were rejected. In total, we found 323 variables, from which 246 are reported here for the first time, and 77 were probably wrongly classified before. The observed variability pattern of most stars is in accordance with an ACV classification. For some cases, it is difficult to distinguish between the light curves of double-waved ACVs and the variability induced by orbital motion (ellipsoidal variables/eclipsing variables), especially for objects exhibiting very small amplitudes and/or significant scatter in their light curves. Thus, some eclipsing or rotating ellipsoidal variables might be present. However, we are confident that the given periods are the correct ones. There seems to be a possible weak correlation between the rotational period and colour, in the sense that cooler magnetic CP stars rotate more slowly. However, this correlation seems to disappear when correcting for the interstellar reddening. The next steps have to include a compilation of all available rotational periods from the literature and a detailed investigation of the astrophysical parameters of these stars. This includes a determination of the individual masses, luminosities, ages, and inclination angles. However, this information cannot be straightforwardly determined from photometric data alone.
- ID:
- ivo://CDS.VizieR/J/AJ/153/252
- Title:
- Photometric variability of BeSS-KELT stars
- Short Name:
- J/AJ/153/252
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Be stars have generally been characterized by the emission lines in their spectra, and especially the time variability of those spectroscopic features. They are known to also exhibit photometric variability at multiple timescales, but have not been broadly compared and analyzed by that behavior. We have taken advantage of the advent of wide-field, long-baseline, and high-cadence photometric surveys that search for transiting exoplanets to perform a comprehensive analysis of brightness variations among a large number of known Be stars. The photometric data comes from the KELT transit survey, with a typical cadence of 30 minutes, a baseline of up to 10 years, photometric precision of about 1%, and coverage of about 60% of the sky. We analyze KELT light curves of 610 known Be stars in both the northern and southern hemispheres in an effort to study their variability. Consistent with other studies of Be star variability, we find most of the stars to be photometrically variable. We derive lower limits on the fraction of stars in our sample that exhibit features consistent with non-radial pulsations (25%), outbursts (36%), and long-term trends in the circumstellar disk (37%), and show how these are correlated with spectral sub-types. Other types of variability, such as those owing to binarity, are also explored. Simultaneous spectroscopy for some of these systems from the Be Star Spectra database allow us to better understand the physical causes for the observed variability, especially in cases of outbursts and changes in the disk.
