Medium-resolution echelle spectroscopy of pulsating variables and exoplanet host stars with sub-meter telescopes

Here we present two of our interesting results obtained over the last 18 months from spectroscopic monitoring of binary pulsating stars and exoplanet host stars. Our investigations are very promising by demonstrating that modern fiber-fed spectrographs open a whole new chapter in the life of small national and university observatories.Comment: 3 pages, 3 figures. To be published in the proceedings of the workshop on "Observing techniques, instrumentation and science for metre-class telescopes", Sep. 2013, Tatranska Lomnica, Slovaki

Photometric observations of 9 Near-Earth Objects

We present new CCD observations of nine Near-Earth Asteroids carried out between February, 1999 and July, 2000. The bulk of the data was acquired through an R_C filter, while the minor planet 11405 was observed without filter. We could determine synodic periods and amplitudes for 5 asteroids, 699: 3.3 h, 0.18 mag; 1866: 2.7 h, 0.12 mag; 1999 JD6: 7.68 h, 1.2 mag; 2000 GK137: 4.84 h, 0.27 mag; 2000 NM: 9.24 h, 0.30 mag. Based on observations taken at different phases, we could infer a phase parameter m of 0.018+/-0.005 for 1865 Cerberus. An epoch-method yielded a sidereal period of 0.27024003(5) d for this object with retrograde rotation. The remaining 3 objects have only partial coverage, thus no firm conclusion on their synodic period is possible

Main-Belt Asteroids in the K2 Engineering Field of View

Unlike NASA's original Kepler Discovery Mission, the renewed K2 Mission will stare at the plane of the Ecliptic, observing each field for approximately 75 days. This will bring new opportunities and challenges, in particular the presence of a large number of main-belt asteroids that will contaminate the photometry. The large pixel size makes K2 data susceptible to the effect of apparent minor planet encounters. Here we investigate the effects of asteroid encounters on photometric precision using a sub-sample of the K2 Engineering data taken in February, 2014. We show examples of asteroid contamination to facilitate their recognition and distinguish these events from other error sources. We conclude that main-belt asteroids will have considerable effects on K2 photometry of a large number of photometric targets during the Mission, that will have to be taken into account. These results will be readily applicable for future space photometric missions applying large-format CCDs, such as TESS and PLATO.Comment: accepted for publication in AJ, 6 page

RR Lyrae stars in the southern globular cluster NGC 362

NGC 362 is a bright southern globular cluster for which no extensive variability survey has ever been done. Time-series CCD photometric observations have been obtained. Light curves have been derived with both profile fitting photometry and image subtraction. We developed a simple method to convert flux phase curves to magnitudes, which allows the use of empirical light curve shape vs. physical parameters calibrations. Using the RR Lyrae metallicity and luminosity calibrations, we have determined the relative iron abundances and absolute magnitudes of the stars. The color-magnitude diagram has been fitted with Yale-Yonsei isochrones to determine reddening and distance independently. For five RR Lyrae stars we obtained radial velocity measurements from optical spectra. We found 45 RR Lyr stars, of which the majority are new discoveries. About half of the RR Lyraes exhibit light curve changes (Blazhko effect). The RR Lyrae-based metallicity of the cluster is [Fe/H]=-1.16 +/- 0.25, the mean absolute magnitude of the RR Lyrae stars is M_V=0.82 +/- 0.04 mag implying a distance of 7.9 +/- 0.6 kpc. The mean period of RRab stars is 0.585 +/- 0.081 days. These properties place NGC 362 among the Oosterhoff type I globular clusters. The isochrone fit implies a slightly larger distance of 9.2 +/- 0.5 kpc and an age of 11 +/- 1 Gyr. We also found 11 eclipsing binaries, 14 pulsating stars of other types, including classical Cepheids in the SMC and 15 variable stars with no firm classification

Discovery of the spectroscopic binary nature of the classical Cepheids FN Aql and V1344 Aql

We present the analysis of photometric and spectroscopic data of two classical Cepheids, FN Aquilae and V1344 Aquilae. Based on the joint treatment of the new and earlier radial velocity data, both Galactic Cepheids have been found to be a member in a spectroscopic binary system. To match the phases of the earlier radial velocity data correctly with the new ones, we also determined the temporal behaviour of the pulsation period of these Cepheids based on all available photometric data. The O-C graph covering about half century shows slight changes in the pulsation period due to stellar evolution for both Cepheids.Comment: 7 pages, 6 figures, 7 tables, accepted for publishing in the MNRA

Investigating magnetic activity in very stable stellar magnetic fields: long-term photometric and spectroscopic study of the fully convective M4 dwarf V374 Peg

The ultrafast-rotating ($P_\mathrm{rot}\approx0.44 d$) fully convective single M4 dwarf V374 Peg is a well-known laboratory for studying intense stellar activity in a stable magnetic topology. As an observable proxy for the stellar magnetic field, we study the stability of the light curve, and thus the spot configuration. We also measure the occurrence rate of flares and coronal mass ejections (CMEs). We analyse spectroscopic observations, $BV(RI)_C$ photometry covering 5 years, and additional $R_C$ photometry that expands the temporal base over 16 years. The light curve suggests an almost rigid-body rotation, and a spot configuration that is stable over about 16 years, confirming the previous indications of a very stable magnetic field. We observed small changes on a nightly timescale, and frequent flaring, including a possible sympathetic flare. The strongest flares seem to be more concentrated around the phase where the light curve indicates a smaller active region. Spectral data suggest a complex CME with falling-back and re-ejected material, with a maximal projected velocity of $\approx$675km/s. We observed a CME rate much lower than expected from extrapolations of the solar flare-CME relation to active stars.Comment: 15 figures, 4 tables, accepted for publication in A&

A variable star survey of the open cluster M37

A CCD photometric study of the dense galactic open cluster M37 is presented and discussed. The majority of the analysed data are time-series measurements obtained through an R_C filter. The observations were carried out on seven nights between December 1999 and February 2000, and have led to the discovery of 7 new variable stars in the field. Three of them have been unambiguously identified as W UMa-type eclipsing binaries, while two more are monoperiodic pulsating stars, most probably high-amplitude delta Scuti-type variables. The remaining two stars seem to be long-period eclipsing binaries without firm period determination. Johnson B and V frames have been used to construct a new colour-magnitude (CM) diagram of the cluster, and to find the locations of the new variable stars. The pulsating variables are most likely background objects. The CM diagram is fitted with recent isochrones yielding the main parameters of the cluster.Comment: 7 pages, 6 figures, accepted for publication in A&