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- ID:
- ivo://CDS.VizieR/J/AJ/159/21
- Title:
- V and Rc light curves of medium-bright PPNe
- Short Name:
- J/AJ/159/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 10 years of new photometric monitoring of the light variability of five evolved stars with strong mid-infrared emission from surrounding dust. Three are known carbon-rich proto-planetary nebulae (PPNe) with F-G spectral types; the nature of the other two was previously unknown. For the three PPNe, we determine or refine the pulsation periods of IRAS04296+3429 (71 days), 06530-0213 (80 days), and 23304+6147 (84 days). A secondary period was found for each, with a period ratio P_2_/P_1_ of 0.9. The light variations are small, 0.1-0.2mag. These are similar to values found in other PPNe. The other two are found to be giant stars. IRAS09296+1159 pulsates with a period of only 47 days but reaches pulsational light variations of 0.5mag. Supplemental spectroscopy reveals the spectrum of a CH carbon star. IRAS08359-1644 is a G1III star that does not display pulsational variability; rather, it shows nonperiodic decreases of brightness of up to 0.5mag over this 10 year interval. These drops in brightness are reminiscent of the light curves of R Corona Borealis variables, but with much smaller decreases in brightness and are likely due to transient dust obscuration. Its spectral energy distribution is very similar to that of the unusual oxygen-rich giant star HDE233517, which possesses mid-infrared hydrocarbon emission features. These two non-PPNe turn out to be members of the rare group of giant stars with large mid-infrared excesses due to dust, objects which presumably have interesting evolutionary histories.
- ID:
- ivo://CDS.VizieR/J/MNRAS/449/2750
- Title:
- V and R lightcurves of BL Lac object PKS 0537-441
- Short Name:
- J/MNRAS/449/2750
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the colour indices V-R of BL Lacertae object PKS 0537-441 on the basis of the photometric data monitored by the Rapid Eye Mounting (REM) telescope located at the ESO Cerro La Silla observatory (Chile). Nearly 700 quasi-simultaneous data groups were collected during the period from 2004 to 2010. Our colour analysis shows the existence of at least two variability mechanisms: one is the long-term chromatic mechanism in which the variation traces a 0.04+/-0.01 slope in the V-R versus V plot, the other is the chromatic mechanism implying the spectral changes during the flares and on intraday time-scales. A general bluer-when-brighter trend is confirmed in both ascent and descent states during the flares and in the 2010 February flare interval, while a much stronger bluer-when-brighter chromatism is observed in both faint and bright states on intraday time-scales. The discrete correlation function analysis reveals the existence of a time-lag of 13^+5.8^_-1.2_ d between colour indices and magnitudes during the period MJD 54404-54453, whereas no measurable time-lag during other periods is found. Our results suggest that geometric effects may be responsible for the long-term achromatic mechanism, while the intrinsic shock-in-jet mechanism may produce the chromatic variability during the flares and on intraday time-scales.
- ID:
- ivo://CDS.VizieR/J/A+A/403/637
- Title:
- V and R light curves of GSC 3822-1056
- Short Name:
- J/A+A/403/637
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Here we present the first Johnson-Cousins VR_C_ light curves of the over-contact binary star GSC 3822-1056. A period study and the light curve solution are also given. An extremely high rate of period increase +11.6sec/century was found. The origin of this period change can be: (i) partly covered light-time effect due to the orbital motion around the mass center of a possible third body; (ii) mass transfer between the components. The light curve was solved by the 1998 Wilson-Devinney Code. We examined the light curve with and without third light. Both solutions yielded a contact configuration with high temperature difference between the components. Despite the high degree of the contact (f=0.57), the temperature difference between the components {Delta}T=T_primary_-T_secondary_=1045K. The high mass-ratio of the system and its other unusual properties suggest that GSC 3822-1056 may be a recently formed contact binary.
- ID:
- ivo://CDS.VizieR/J/other/CoSka/40.19
- Title:
- V466 And UBV(RI)c light curves
- Short Name:
- J/other/CoSka/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the UBV(RI)C photometry of a new dwarf nova V466 And, discovered during its superoutburst on Sept. 1.6, 2008 and classified as a WZ Sge-type object. In the first 11 days of the superoutburst, the early superhumps with the period of 0.056383d were found. In days 13-23 of the superoutburst, the ordinary superhumps with the period of 0.05713d were exposed. They were replaced by late superhumps with the period of 0.056d in days 24-33 of the superoutburst. After one month, the dwarf nova returned to its pre-outburst state. A list of known WZ Sge-type dwarf novae, including suspected ones, is presented. We determined a mean value of superhump period excess for WZ Sge-type objects as {epsilon}=0.019+/-0.003. The multicolour photometry of the field stars enables us to conclude that there is no appreciable interstellar extinction in the direction of V466 And.
- ID:
- ivo://CDS.VizieR/J/A+A/550/A120
- Title:
- Variability classification of CoRoT targets
- Short Name:
- J/A+A/550/A120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an improved method for automated stellar variability classification, using fundamental parameters derived from high resolution spectra, with the goal to improve the variability classification obtained using information derived from CoRoT light curves only. Although we focus on Giraffe spectra and CoRoT light curves in this work, the methods are much more widely applicable. In order to improve the variability classification obtained from the photometric time series, only rough estimates of the stellar physical parameters (Teff and logg) are needed because most variability types that overlap in the space of time series parameters, are well separated in the space of physical parameters (e.g. {gamma} Dor/SPB or {delta} Sct/{beta} Cep). In this work, several state-of-the-art machine learning techniques are combined to estimate these fundamental parameters from high resolution Giraffe spectra. Next, these parameters are used in a multi-stage Gaussian-Mixture classifier to perform an improved supervised variability classification of CoRoT light curves. The variability classifier can be used independently of the regression module that estimates the physical parameters, so that non-spectroscopic estimates derived e.g. from photometric colour indices can be used instead. Teff and logg are derived from Giraffe spectra, for 6832 CoRoT targets. The use of those parameters in addition to information extracted from the CoRoT light curves, significantly improves the results of our previous automated stellar variability classification. Several new pulsating stars are identified with high confidence levels, including hot pulsators such as SPB and {beta} Cep, and several {gamma} Dor-{delta} Sct hybrids. From our samples of new {gamma} Dor and {delta} Sct stars, we find strong indications that the instability domains for both types of pulsators are larger than previously thought.
- ID:
- ivo://CDS.VizieR/J/ApJ/709/1042
- Title:
- Variability in C-rich proto-PNe.
- Short Name:
- J/ApJ/709/1042
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out long-term (14 years) V and R photometric monitoring of 12 carbon-rich proto-planetary nebulae. The light and color curves display variability in all of them. The light curves are complex and suggest multiple periods, changing periods, and/or changing amplitudes, which are attributed to pulsation. A dominant period has been determined for each and found to be in the range of ~150 days for the coolest (G8) to 35-40 days for the warmest (F3). A clear, linear inverse relationship has been found in the sample between the pulsation period and the effective temperature and also an inverse relationship between the amplitude of light variation and the effective temperature. These are consistent with the expectation for a pulsating post-asymptotic giant branch (post-AGB) star evolving toward higher temperature at constant luminosity. The published spectral energy distributions and mid-infrared images show these objects to have cool (200K), detached dust shells and published models imply that intensive mass loss ended 400-2000 years ago.
- ID:
- ivo://CDS.VizieR/J/A+A/525/A37
- Title:
- Variability indexes of QSOs in SDSS Stripe 82
- Short Name:
- J/A+A/525/A37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identified 8744 quasars in the Light-Motion Curve Catalogue (LMCC; Bramich et al., 2008MNRAS.386..887B, http://das.sdss.org/value_added/stripe_82_variability/SDSS_82_public/) for the stripe 82 of the Sloan Digital Sky Survey (SDSS). The light curves were used, after correction for photometric outliers, to compute individual noise-corrected first-order structure functions (variance as a function of time-lag) binned into rest frame time-lag intervals. The mean value of the corrected structure function at rest frame time-lags from 300 to 600 days is found to be a useful variability index for the statistical investigation of quasar samples with redshifts up to ~3. For each quasar, the variability indexes for the five SDSS bands are given along with the equatorial coordinates, redshift, mean g band magnitude, absolute i band magnitude, and a remark on spectral peculiarities.
- ID:
- ivo://CDS.VizieR/J/ApJ/901/9
- Title:
- Variability in protoplanetary nebulae. VII. 5 LCs
- Short Name:
- J/ApJ/901/9
- Date:
- 15 Feb 2022 13:25:51
- Publisher:
- CDS
- Description:
- We have monitored over a 10-year interval the light variations of five evolved stars with very large mid-infrared excesses. All five objects appear to have oxygen-rich or mixed oxygen-rich and carbon-rich chemistries. They all vary in light: four over a small range of ~0.2mag and the fifth over a larger range of ~0.7mag. Spectral types range from G2 to B0. Periodic pulsations are found for the first time in the three cooler ones, IRAS18075-0924 (123d), 19207+2023 (96d), and 20136+1309 (142d). No significant periodicity is found in the hotter ones, but they appear to vary on a shorter timescale of a few days or less. Two also show some evidence of longer-term periodic variations (~4yr). Three appear to be protoplanetary nebulae (PPNe), in the post-asymptotic giant branch (post-AGB) phase of stellar evolution. Their light variations are in general agreement with the relationships among temperature, pulsation period, and pulsation amplitude found in previously studied PPNe. The other two, however, appear to have too low a luminosity (1000-1500L_{sun}_), based on Gaia distances, to be in the post-AGB phase. Instead, they appear to be Milky Way analogs of the recently identified class of dusty post-red giant branch (post-RGB) stars found in the Magellanic Clouds, which likely had their evolution interrupted by interaction with a binary companion. If this is the case, then these would be among the first dusty post-RGB objects identified in the the Milky Way.
- ID:
- ivo://CDS.VizieR/J/ApJ/766/116
- Title:
- Variability in proto-PNe. II.
- Short Name:
- J/ApJ/766/116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out a detailed observational study of the light, color, and velocity variations of two bright, carbon-rich proto-planetary nebulae, IRAS 22223+4327 and 22272+5435. The light curves are based upon our observations from 1994 to 2011, together with published data by Arkhipova and collaborators. They each display four significant periods, with primary periods for IRAS 22223+4327 and 22272+5435 being 90 and 132 days, respectively. For each of them, the ratio of secondary to primary period is 0.95, a value much different from that found in Cepheids, but which may be characteristic of post-asymptotic giant branch (AGB) stars. Fewer significant periods are found in the smaller radial velocity data sets, but they agree with those of the light curves. The color curves generally mimic the light curves, with the objects reddest when faintest. A comparison in seasons when there exist contemporaneous light, color, and velocity curves reveals that the light and color curves are in phase, while the radial velocity curves are ~0.25 P out of phase with the light curves. Thus they differ from what is seen in Cepheids, in which the radial velocity curve is 0.50 P out of phase with the light curve. Comparison of the observed periods and amplitudes with those of post-AGB pulsation models shows poor agreement, especially for the periods, which are much longer than predicted. These observational data, particularly the contemporaneous light, color, and velocity curves, provide an excellent benchmark for new pulsation models of cool stars in the post-AGB, proto-planetary nebula phase.
