G 207-9 and LP 133-144 are two rarely observed ZZ Ceti stars located in the middle and close to the blue edge of the ZZ Ceti instability domain, respectively. We aimed to observe them at least during one observing season at Konkoly Observatory with the purpose of extending the list of known pulsation modes for asteroseismic investigations and detect any significant changes in their pulsational behaviour. We determined five and three new normal modes of G 207-9 and LP 133-144, respectively. In LP 133-144, our frequency analysis also revealed that at least at three modes there are actually triplets with frequency separations of ~4Hz. The rotational period of LP 133-144 based on the triplets is ~=42h. The preliminary asteroseismic fits of G 207-9 predict Teff=12000 or 12400K and M=0.855--0.870M_{sun}_ values for the effective temperature and mass of the star, depending on the assumptions on the spherical degree (l) values of the modes. These results are in agreement with the spectroscopic determinations. In the case of LP 133-144, the best-fitting models prefer Teff=11800K in effective temperature and M*>=0.71M_{sun}_ stellar masses, which are more than 0.1M_{sun}_ larger than the spectroscopic value.
Adopted line data, measured equivalent widths and derived elemental abundances for the individual lines observed in R Coronae Borealis and Extreme Helium stars.
We use V-band time-series data to analyze the RR Lyrae (RRL) population of the Galactic globular cluster NGC 6101. Using template fitting, we have discovered seven new RRL stars and confirmed 10 candidates. We find unusually long mean periods for the RRL of <P_ab_>=0.803 days and <P_c_>=0.393 days, and an atypically high ratio of n(c)/n(ab+c)=0.82. Based on our derived mean properties of the RRL, NGC 6101 is Oosterhoff type II, consistent with the cluster metallicity but intriguing with respect to its kinematics.
The "VISTA near-infrared YJK_s_ survey of the Magellanic Clouds System" (VMC) is collecting deep K_s_-band time-series photometry of pulsating variable stars hosted by the two Magellanic Clouds and their connecting Bridge. In this paper, we present Y, J, K_s_ light curves for a sample of 4172 Small Magellanic Cloud (SMC) Classical Cepheids (CCs). These data, complemented with literature V values, allowed us to construct a variety of period-luminosity (PL), period-luminosity-color (PLC), and period-Wesenheit (PW) relationships, which are valid for Fundamental (F), First Overtone (FO), and Second Overtone (SO) pulsators. The relations involving the V, J, K_s_ bands are in agreement with their counterparts in the literature. As for the Y band, to our knowledge, we present the first CC PL, PW, and PLC relations ever derived using this filter. We also present the first near-infrared PL, PW, and PLC relations for SO pulsators to date. We used PW(V, K_s_) to estimate the relative SMC-LMC distance and, in turn, the absolute distance to the SMC. For the former quantity, we find a value of {Delta}{mu}=0.55+/-0.04mag, which is in rather good agreement with other evaluations based on CCs, but significantly larger than the results obtained from older population II distance indicators. This discrepancy might be due to the different geometric distributions of young and old tracers in both Clouds. As for the absolute distance to the SMC, our best estimates are {mu}_SMC_=19.01+/-0.05mag and {mu}_SMC_=19.04+/-0.06mag, based on two distance measurements to the LMC which rely on accurate CC and eclipsing Cepheid binary data, respectively.
Time-varying phenomena are one of the most substantial sources of astrophysical information, and their study has led to many fundamental discoveries in modern astronomy. We have developed an automated tool to search for and analyze variable sources in the near-infrared Ks band using the data from the VISTA Variables in the Via Lactea (VVV) ESO Public Large Survey. This process relies on the characterization of variable sources using different variability indices calculated from time series generated with point-spread function (PSF) photometry of sources under analysis. In particular, we used two main indices, the total amplitude {Delta}Ks and the eta index {eta}, to identify variable sources. Once the variable objects are identified, periods are determined with generalized Lomb-Scargle periodograms and the information potential metric. Variability classes are assigned according to a compromise between comparisons with VVV templates and the period of the variability. The automated tool is applied on VVV tiles d001 and d002 and led to the discovery of 200 variable sources. We detected 70 irregular variable sources and 130 periodic ones. In addition, nine open-cluster candidates projected in the region are analyzed, and the infrared variable candidates found around these clusters are further scrutinized by cross-matching their locations against emission star candidates from VPHAS+ survey H{alpha} color cuts.
We present the next regular Name-List of variable stars containing information on 1706 variable stars recently designated in the system of the General Catalogue of Variable Stars.
We present the special Name-List of variable stars containing information on 1270 variable stars recently designated in the system of the General Catalogue of Variable Stars, which are mostly former suspected variables from the NSV catalogue.
We present the first part of a new Name-List of variable stars containing information on 1951 variable stars recently designated in the system of the General Catalogue of Variable Stars. With the exception of Novae and other unusual variables named upon request from the IAU CBAT or by our initiative, these stars are in the range of J2000.0 right ascensions from 0 hours to 17 hours 30 minutes.
We present the first part of a new Name-List of variable stars containing information on 2036 variable stars recently designated in the system of the General Catalogue of Variable Stars. With the exception of unusual variables named upon request from the IAU CBAT, these stars are in the range of J2000.0 right ascensions from 0 to 6 hours.
We present the second part of a new Name-List of variable stars containing information on 2090 variable stars recently designated in the system of the General Catalogue of Variable Stars. All these stars are in the range of J2000.0 right ascensions from 17 hours 30 minutes to 24 hours.
