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16591. V and R CCD photometry of visual binaries
ID:
ivo://CDS.VizieR/J/A+A/416/811
Title:
V and R CCD photometry of visual binaries
Short Name:
J/A+A/416/811
Date:
21 Oct 2021
Publisher:
CDS
Description:
429 CCD measurements of relative positions and magnitude differences in V and R photometric bands for 165 visual double and multiple stars are given. CCD frames were taken at the 1.52m Spanish telescope of the Spanish-German Center of Astronomy at Calar Alto (Almeria, Spain). During the reduction process a "Tepui" function was used as the PSF function.
16592. V and Rc light curves of medium-bright PPNe
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.
16593. Vanishing and appearing sources using USNO data
ID:
ivo://CDS.VizieR/J/AJ/159/8
Title:
Vanishing and appearing sources using USNO data
Short Name:
J/AJ/159/8
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this paper we report the current status of a new research program. The primary goal of the "Vanishing and Appearing Sources during a Century of Observations" project is to search for vanishing and appearing sources using existing survey data to find examples of exceptional astrophysical transients. The implications of finding such objects extend from traditional astrophysics fields to the more exotic searches for evidence of technologically advanced civilizations. In this first paper we present new, deeper observations of the tentative candidate discovered by Villarroel et al. (2016AJ....152...76V). We then perform the first searches for vanishing objects throughout the sky by comparing 600 million objects from the US Naval Observatory Catalogue (USNO) B1.0 (Cat. I/284) down to a limiting magnitude of ~20-21 with the recent Pan-STARRS Data Release-1 (DR1, Cat. II/349) with a limiting magnitude of ~23.4. We find about 150000 preliminary candidates that do not have any Pan-STARRS counterpart within a 30" radius. We show that these objects are redder and have larger proper motions than typical USNO objects. We visually examine the images for a subset of about 24000 candidates, superseding the 2016 study with a sample 10 times larger. We find about 100 point sources visible in only one epoch in the red band of the USNO, which may be of interest in searches for strong M-dwarf flares, high-redshift supernovae, or other categories of unidentified red transients.
16594. (174567) Varda multi-chord stellar occultation
ID:
ivo://CDS.VizieR/J/A+A/643/A125
Title:
(174567) Varda multi-chord stellar occultation
Short Name:
J/A+A/643/A125
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present here results of the first-ever recorded stellar occultation by the large trans-Neptunian object (174567) Varda that was observed on September 10th, 2018. Varda belongs to the high-inclination dynamically excited population, and has a satellite, Ilmare, which is half the size of Varda.
16595. Variability and spectra of LMC giants
ID:
ivo://CDS.VizieR/J/A+A/377/945
Title:
Variability and spectra of LMC giants
Short Name:
J/A+A/377/945
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the first cross-identifications of sources in the near-infrared DENIS survey and in the micro-lensing EROS survey in a field of about 0.5 square degrees around the optical center (OC) of the Large Magellanic Cloud. We analyze the photometric history of these stars in the EROS data base and obtain light-curves for about 800 variables. Most of the stars are long period variables (Miras and Semi-Regulars); a few Cepheids are also present. We also present new spectroscopic data on 126 asymptotic giant branch stars in the OC field, 30 previously known and 96 newly discovered by the DENIS survey. The visible spectra are used to assign a carbon- (C-) or oxygen-rich (O-rich) nature to the observed stars on the basis of the presence of molecular bands of TiO, VO, CN, C_2_. For the remaining of the stars we used the (J-K_S_) color to determine whether they are O-rich or C-rich. Plotting Log(period) versus K_S_ we find three very distinct period-luminosity relations, mainly populated by Semi-Regular stars of type a (SRa), b (SRb) and Mira variables. Carbon-rich stars occupy mostly the upper part of these relations. We find that 65% of the asymptotic giant branch population are long period variables (LPVs).
16596. Variability at Frequencies 3.9 and 7.5 GHz
ID:
ivo://CDS.VizieR/J/AZh/72/291
Title:
Variability at Frequencies 3.9 and 7.5 GHz
Short Name:
J/AZh/72/291
Date:
21 Oct 2021
Publisher:
CDS
Description:
A complete sample of radio sources from the Zelenchukskii survey with fluxes S(3.9GHz)>200mJy and declination range from +4 till +6 degrees were observed at 3.9 and 7.5GHz over the course of seven years. There are one hundred and eighty radio sources in the sample.
16597. Variability classification of CoRoT targets
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.
16598. Variability components in BATSE GRB light curves
ID:
ivo://CDS.VizieR/J/ApJ/748/134
Title:
Variability components in BATSE GRB light curves
Short Name:
J/ApJ/748/134
Date:
21 Oct 2021
Publisher:
CDS
Description:
Gamma-ray bursts (GRBs) have variable light curves. Although most models attribute the observed variability to one physical origin (e.g., central engine activity, clumpy circumburst medium, or relativistic turbulence), some models invoke two physically distinct variability components. We develop a method, namely, the stepwise filter correlation method, to decompose the variability components in a GRB light curve. Based on a low-pass filter technique, we progressively filter the high-frequency signals from the light curve, and then perform a correlation analysis between each adjunct pair of filtered light curves. Our simulations suggest that if a mock light curve contains a "slow" variability component superposed on a rapidly varying time sequence, the correlation coefficient as a function of the filter frequency would display a prominent "dip" feature around the frequency of the slow component. Through simulations, we demonstrate that this method can identify significant clustering structures of a light curve in the frequency domain, and we prove that it can catch superposed signals that are otherwise not easy to retrieve based on other methods (e.g., the power density spectrum analysis method). We apply this method to 266 Burst and Transient Source Experiment bright GRBs. We find that the majority of the bursts have clear evidence of such a superposition effect. We perform a statistical analysis of the identified variability components and discuss the implications for GRB physics.
16599. Variability in C-rich proto-PNe.
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.
16600. Variability indexes of QSOs in SDSS Stripe 82
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.

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