- ID:
- ivo://CDS.VizieR/J/AJ/150/32
- Title:
- KELT 2006-2013 photometry of V409 Tau and AA Tau
- Short Name:
- J/AJ/150/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- AA Tau is a well studied young stellar object (YSO) that presents many of the photometric characteristics of a Classical T Tauri star (CTTS), including short-timescale stochastic variability attributed to spots and/or accretion as well as long-duration dimming events attributed to occultations by vertical features (e.g., warps) in its circumstellar disk. We present new photometric observations of AA Tau from the Kilodegree Extremely Little Telescope North (KELT-North) which reveal a deep, extended dimming event in 2011, which we show supports the interpretation by Bouvier et al. of an occultation by a high-density feature in the circumstellar disk located >8AU from the star. We also present KELT-North observations of V409 Tau, a relatively unstudied YSO also in Taurus-Auriga, showing short timescale erratic variability, along with two separate long and deep dimming events, one from 2009 January through late 2010 October, and the other from 2012 March until at least 2013 September. We interpret both dimming events to have lasted more than 600 days, each with a depth of ~1.4mag. From a spectral energy distribution analysis, we propose that V409 Tau is most likely surrounded by a circumstellar disk viewed nearly edge-on, and using Keplerian timescale arguments we interpret the deep dimmings of V409 Tau as occultations from one or more features within this disk >~10AU from the star. In both AA Tau and V409 Tau, the usual CTTS short-timescale variations associated with accretion processes close to the stars continue during the occultations, further supporting the distant occulting material interpretation. Like AA Tau, V409 Tau serves as a laboratory for studying the detailed structure of the protoplanetary environments of T Tauri disks, specifically disk structures that may be signposts of planet formation at many AU out in the disk. We also provide a table of all currently known disk-occulting young stars as a convenient reference for future work on such objects.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/414/2860
- Title:
- Kepler compact pulsator candidates
- Short Name:
- J/MNRAS/414/2860
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from the final 6 months of a survey to search for pulsations in white dwarfs (WDs) and hot subdwarf stars with the Kepler spacecraft. Spectroscopic observations are used to separate the objects into accurate classes, and we explore the physical parameters of the subdwarf B (sdB) stars and white dwarfs in the sample. From the Kepler photometry and our spectroscopic data, we find that the sample contains five new pulsators of the V1093 Her type, one AM CVn type cataclysmic variable and a number of other binary systems.
- ID:
- ivo://CDS.VizieR/J/AJ/143/4
- Title:
- Kepler cycle 1 observations of low-mass stars
- Short Name:
- J/AJ/143/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed Kepler light curves for 849 stars with Teff<=5200K from our Cycle 1 Guest Observer program. We identify six new eclipsing binaries, one of which has an orbital period of 29.91 days and two of which are probably W UMa variables. In addition, we identify a candidate "warm Jupiter" exoplanet. We further examine a subset of 670 sources for variability. Of these objects, 265 stars clearly show periodic variability that we assign to rotation of the low-mass star. At the photometric precision level provided by Kepler, 251 of our objects showed no evidence for variability. We were unable to determine periods for 154 variable objects. We find that 79% of stars with Teff<=5200K are variable. The rotation periods we derive for the periodic variables span the range 0.31days<=Prot<=126.5days. A considerable number of stars with rotation periods similar to the solar value show activity levels that are 100 times higher than the Sun.
- ID:
- ivo://CDS.VizieR/J/MNRAS/460/1970
- Title:
- Kepler {delta} Sct stars amplitude modulation
- Short Name:
- J/MNRAS/460/1970
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a thorough search for amplitude modulation of pulsation modes in 983 {delta} Sct stars, which have effective temperatures between 6400<T_eff_<10000K in the Kepler Input Catalogue and were continuously observed by the Kepler Space Telescope for 4yr. We demonstrate the diversity in pulsational behaviour observed, in particular non-linearity, which is predicted for {delta} Sct stars. We analyse and discuss examples of {delta} Sct stars with constant amplitudes and phases; those that exhibit amplitude modulation caused by beating of close-frequency pulsation modes; those that exhibit pure amplitude modulation (with no associated phase variation); those that exhibit phase modulation caused by binarity; and those that exhibit amplitude modulation caused by non-linearity. Using models and examples of individual stars, we demonstrate that observations of the changes in amplitude and phase of pulsation modes can be used to distinguish among the different scenarios. We find that 603 {delta} Sct stars (61.3 per cent) exhibit at least one pulsation mode that varies significantly in amplitude over 4yr. Conversely, many {delta} Sct stars have constant pulsation amplitudes so short-length observations can be used to determine precise frequencies, amplitudes and phases for the most coherent and periodic {delta} Sct stars. It is shown that amplitude modulation is not restricted to a small region on the HR diagram, therefore not necessarily dependent on stellar parameters such as T_eff_, logg or [Fe/H]. Our catalogue of 983 {delta} Sct stars will be useful for comparisons to similar stars observed by K2 and TESS, because the length of the 4-yr Kepler data set will not be surpassed for some time.
- ID:
- ivo://CDS.VizieR/J/ApJ/820/1
- Title:
- Kepler light curve of the EB star KIC 9532219
- Short Name:
- J/ApJ/820/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- KIC 9532219 is a W UMa-type eclipsing binary with an orbital period of 0.1981549days that is below the short-period limit (~0.22days) of the period distribution for contact binaries. The Kepler light curve of the system exhibits striking changes in both eclipse depths and light maxima. Applying third-body and spot effects, the light-curve synthesis indicates that the eclipsing pair is currently in a marginal contact stage with a mass ratio of q=1.20, an orbital inclination of i=66.0{deg}, a temperature difference of T_1_-T_2_=172K, and a third light of l_3_=75.9%. To understand the light variations with time, we divided up the light curve into 312 segments and analyzed them separately. The results reveal that variation of eclipse depth is primarily caused by changing amounts of contamination due to the nearby star KIC 9532228 between the Kepler Quarters and that the variable O'Connell effect originates from the starspot activity on the less massive primary component. Based on our light-curve timings, a period study of KIC 9532219 indicates that the orbital period has varied as a combination of a downward parabola and a light-travel-time (LTT) effect due to a third body, which has a period of 1196 days and a minimum mass of 0.0892M_{sun}_ in an orbit of eccentricity 0.150. The parabolic variation could be a small part of a second LTT orbit due to a fourth component in a wider orbit, instead of either mass transfer or angular momentum loss.
- ID:
- ivo://CDS.VizieR/J/AJ/142/160
- Title:
- Kepler Mission. II. Eclipsing binaries in DR2
- Short Name:
- J/AJ/142/160
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Kepler Mission (launched in 2009 March) provides nearly continuous monitoring of ~156000 objects with unprecedented photometric precision. Coincident with the first data release, we presented a catalog of 1879 eclipsing binary systems identified within the 115deg^2^ Kepler field of view (FOV). Here, we provide an updated catalog from paper I (Prsa et al. 2011, Cat. J/AJ/141/83) augmented with the second Kepler data release which increases the baseline nearly fourfold to 125 days. Three hundred and eighty-six new systems have been added, ephemerides and principal parameters have been recomputed. We have removed 42 previously cataloged systems that are now clearly recognized as short-period pulsating variables and another 58 blended systems where we have determined that the Kepler target object is not itself the eclipsing binary. A number of interesting objects are identified. We present several exemplary cases: four eclipsing binaries that exhibit extra (tertiary) eclipse events; and eight systems that show clear eclipse timing variations indicative of the presence of additional bodies bound in the system. We have updated the period and galactic latitude distribution diagrams. With these changes, the total number of identified eclipsing binary systems in the Kepler FOV has increased to 2165, 1.4% of the Kepler target stars.
- ID:
- ivo://CDS.VizieR/J/A+A/529/A89
- Title:
- Kepler satellite variability study
- Short Name:
- J/A+A/529/A89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an automated variability analysis of the Kepler public data measured in the first quarter (Q1) of the mission. In total, about 150000 light curves have been analysed to detect stellar variability, and to identify new members of known variability classes. We also focus on the detection of variables present in eclipsing binary systems, given the important constraints on stellar fundamental parameters they can provide. The methodology we use here is based on the automated variability classification pipeline which was previously developed for and applied successfully to the CoRoT exofield database and to the limited subset of a few thousand Kepler asteroseismology light curves. We use a Fourier decomposition of the light curves to describe their variability behaviour and use the resulting parameters to perform a supervised classification. Several improvements have been made, including a separate extractor method to detect the presence of eclipses when other variability is present in the light curves. We also included two new variability classes compared to previous work: variables showing signs of rotational modulation and of activity. Statistics are given on the number of variables and the number of good candidates per class. A comparison is made with results obtained for the CoRoT exoplanet data. We present some special discoveries, including variable stars in eclipsing binary systems. Many new candidate non-radial pulsators are found, mainly Delta Sct and Gamma Dor stars. We have studied those samples in more detail by using 2MASS colours. The full classification results are made available as an online catalogue.
- ID:
- ivo://CDS.VizieR/J/MNRAS/429/1466
- Title:
- Kepler stars in the NGC 6866 field
- Short Name:
- J/MNRAS/429/1466
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of stars in the field of the open cluster NGC 6866 (age 650Myr) using data from the Kepler Input Catalogue (KIC) and time series photometry from the Kepler data base. We identify 31 {delta} Scuti and 8 {gamma} Doradus pulsating variables as well as 23 red giants with solar-like oscillations. There are 4 eclipsing binaries and 106 stars showing rotational modulation indicative of starspots. We attempted to identify cluster members using their proper motions but found very poor discrimination between members and non-members. The KIC shows a concentration of stars with distance modulus V_0_-M_V_=10.47+/-0.02. We used assumed radial modes in 9 {delta} Sct stars to determine their asteroseismic luminosities and found that the distance modulus falls within three narrow ranges depending on the assignment of overtone number. One of these ranges coincides with the KIC distance modulus. The rotation periods of main-sequence stars are correlated with colour, so that a period-age-mass relation can be derived from open clusters and applied to stars of unknown ages. Surprisingly, we find that the correlation applies not only to cool stars, but extends to A-type stars in the cluster. Finally, we present measurements of solar-like oscillations in red giants, a few of which might be cluster members.
- ID:
- ivo://CDS.VizieR/J/MNRAS/472/1618
- Title:
- Kepler study of starspot lifetimes
- Short Name:
- J/MNRAS/472/1618
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Wide-field high-precision photometric surveys such as Kepler have produced reams of data suitable for investigating stellar magnetic activity of cooler stars. Starspot activity produces quasi-sinusoidal light curves whose phase and amplitude vary as active regions grow and decay over time. Here we investigate, first, whether there is a correlation between the size of starspots - assumed to be related to the amplitude of the sinusoid - and their decay time-scale and, secondly, whether any such correlation depends on the stellar effective temperature. To determine this, we computed the auto-correlation functions of the light curves of samples of stars from Kepler and fitted them with apodised periodic functions. The light-curve amplitudes, representing spot size, were measured from the root-mean-squared scatter of the normalized light curves. We used a Monte Carlo Markov Chain to measure the periods and decay time-scales of the light curves. The results show a correlation between the decay time of starspots and their inferred size. The decay time also depends strongly on the temperature of the star. Cooler stars have spots that last much longer, in particular for stars with longer rotational periods. This is consistent with current theories of diffusive mechanisms causing starspot decay. We also find that the Sun is not unusually quiet for its spectral type - stars with solar-type rotation periods and temperatures tend to have (comparatively) smaller starspots than stars with mid-G or later spectral types.
- ID:
- ivo://CDS.VizieR/J/ApJ/853/77
- Title:
- KIC 8462852 ASAS V-band long-term variability
- Short Name:
- J/ApJ/853/77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present ~800 days of photometric monitoring of Boyajian's Star (KIC8462852) from the All-Sky Automated Survey for Supernovae (ASAS-SN) and ~4000d of monitoring from the All Sky Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian's Star has steadily decreased at a rate of 6.3+/-1.4mmag/yr, such that the star is now 1.5% fainter than it was in 2015 February. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian's Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a monotonic decline. We analyze a sample of ~1000 comparison stars of similar brightness located in the same ASAS-SN field and demonstrate that the recent fading is significant at >=99.4% confidence. The 2015-2017 dimming rate is consistent with that measured with Kepler data for the time period from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models for the star's behavior proposed to date.
