Discovery of 5 Minutes Sine-like Oscillations in the light curve of the Asteroid 1689 Floris-Jan

We present CCD photometry of the long period asteroid 1689 Floris-Jan. On the light curve from nights 1997.02.10/11 and 1997.02.11/12 we detected sine-like oscillations with the period P=4.98 ${\pm}$ 0.01 minutes and full amplitude about 0.11 mag. Observations from night 1997.03.07/08 show no light variations at this period.Comment: submitted to Acta Astronomica, 5 pages, 4 figure

A photometric survey for variable stars in the globular cluster M5

We present the results of a photometric survey for variable stars in the nearby globular cluster M5. A 14.8x22.8 arcmin^2 field centered on the cluster was monitored for a total of 37 hours with a CCD camera mounted on the 1.0-m Swope telescope. Five new variables were identified: four blue stragglers which are SX Phe pulsating variables, and an eclipsing binary with an orbital period of 0.466 d. The eclipsing binary lies near the main-sequence turnoff on the cluster color-magnitude diagram. We do not confirm the variability of any of the 10 eclipsing binaries identified in the cluster field by Reid (1996) and Yan & Reid (1996). The dwarf nova M5-V101 exhibited two outbursts with full amplitudes of about 2.7 mag during our observations. A V/B-V color-magnitude diagram of the surveyed field was obtained, and a possible extreme HB star located 2 mag below cutoff of the blue HB was identified.Comment: 15 pages, LaTex, 11 encapsulated Postscript figures; accepted for publication in A&

The Clusters AgeS Experiment (CASE). Variable stars in the field of the open cluster NGC 6253

The field of the metal-rich open cluster NGC 6253 has been surveyed in a search for variable stars. A total of 25 new variables were detected, 14 of which are bright stars with 13<V<15 mag. This domain was not covered in an earlier work by de Marchi et al. (2010). Four variables, including three short-period eclipsing binaries, are candidate blue straggler stars. Two new detached eclipsing binaries at the turnoff of the cluster and another one on the subgiant branch were identified. These three systems deserve a detailed follow-up study aimed at a determination of the age and distance of NGC 6253. New photometry for 132 stars from the sample of de Marchi et al. (2010) is provided.Comment: Accepted by Acta Astronomic

The Clusters AgeS Experiment (CASE): Variable Stars in the Globular Cluster 47 Tucanae

Based on over 5400 BV images of 47 Tuc collected between 1998 and 2010 we obtained light curves of 65 variables, 21 of which are newly detected objects. New variables are located mostly just outside of the core in a region poorly studied by earlier surveys of the cluster. Among them there are four detached eclipsing binaries and five likely optical counterparts of X-ray sources. Two detached systems are promising targets for follow-up observations. We briefly discuss properties of the most interesting new variables.Comment: Accepted by Acta Astronomic

The Clusters AgeS Experiment (CASE). Variable stars in the field of the globular cluster NGC 6362

The field of the globular cluster NGC 6362 was monitored between 1995 and 2009 in a search for variable stars. BV light curves were obtained for 69 periodic variables including 34 known RR Lyr stars, 10 known objects of other types and 25 newly detected variables. Among the latter we identified 18 proper-motion members of the cluster: seven detached eclipsing binaries (DEBs), six SX Phe stars, two W UMa binaries, two spotted red giants, and a very interesting eclipsing binary composed of two red giants - the first example of such a system found in a globular cluster. Five of the DEBs are located at the turnoff region, and the remaining two are redward of the lower main sequence. Eighty-four objects from the central 9x9 arcmin^2 of the cluster were found in the region of cluster blue stragglers. Of these 70 are proper motion (PM) members of NGC 6362 (including all SX Phe and two W UMa stars), and five are field stars. The remaining nine objects lacking PM information are located at the very core of the cluster, and as such they are likely genuine blue stragglers.Comment: Accepted by Acta Astronomic

A ground-based proper motion study of twelve nearby Globular Clusters

We derive relative proper motions of stars in the fields of the globular clusters M12, NGC 6362, M4, M55, M22, NGC 6752, NGC 3201, M30, M10, NGC 362, M5, and 47 Tucanae based on data collected between 1997 and 2015 with the 1-m Swope telescope of Las Campanas Observatory. We determine membership class and membership probability for over 446 000 objects, and show that these are efficient methods for separating field stars from members of the cluster. In particular, membership probabilities of variable stars and blue/yellow/red stragglers are determined. Finally, we find absolute proper motions for six globular clusters from our sample: M55, NGC 3201, M10, NGC 362, M5, and 47 Tuc. An electronic catalogue of the derived proper motions is publicly available via the internet.Comment: 24 pages, 35 figures, 6 tables. Accepted for publication in MNRAS. Figures of high quality on reques

The Cluster AgeS Experiment (CASE). Variable stars in the field of the globular cluster M22

The field of the globular cluster M22 (NGC 6656) was monitored between 2000 and 2008 in a search for variable stars. $BV$ light curves were obtained for 359 periodic, likely periodic, and long-term variables, 238 of which are new detections. Thirty nine newly detected variables, and 63 previously known ones are members or likely members of the cluster, including 20 SX Phe, 10 RRab and 16 RRc-type pulsators, one BL Her-type pulsator, 21 contact binaries, and 9 detached or semi-detached eclipsing binaries. The most interesting among the identified objects are V112 - a bright multimode SX Phe pulsator, V125 - a $\beta$ Lyr-type binary on the blue horizontal branch, V129 - a blue/yellow straggler with a W UMa-like light curve, located halfway between the extreme horizontal branch and red giant branch, and V134 - an extreme horizontal branch object with $P=2.33$ d and a nearly sinusoidal light curve; all four of them are proper motion (PM) members of the cluster. Among nonmembers, a $P=2.83$ d detached eclipsing binary hosting a $\delta$ Sct-type pulsator was found, and a peculiar $P=0.93$ d binary with ellipsoidal modulation and narrow minimum in the middle of one of the descending shoulders of the sinusoid. We also collected substantial new data for previously known variables; in particular we revise the statistics of the occurrence of the Blazhko effect in RR Lyr-type variables of M22.Comment: 21 pages, 8 figures, 3 table

Absolute parameters of AE For -- a highly active detached binary of late K type

We present photometric and spectroscopic analysis of AE For -- a detached eclipsing binary composed of two late K dwarfs. The masses of the components are found to be 0.6314 +- 0.0035 and 0.6197 +- 0.0034 Msun and the radii to be 0.67 +- 0.03 and 0.63$ +- 0.03 Rsun for primary and secondary component, respectively. Both components are significantly oversized compared to theoretical models, which we attribute to their high activity. They show Halpha, Hbeta, Hgamma, Ca H and Ca K lines in emission, and are heavily spotted, causing large variations of the light curve.Comment: Accepted by MNRA

BVRI Observations of the Optical Afterglow of GRB 990510

We present $BVRI$ observations of the optical counterpart to the Gamma-Ray Burst (GRB) 990510 obtained with the Las Campanas 1.0-m telescope between 15 and 48 hours after the burst. The temporal analysis of the data indicates steepening decay, independent of wavelength, approaching asymptotically $t^{-0.76\pm 0.01}$ at early times ($t\ll 1 day)$ and $t^{-2.40\pm 0.02}$ at late times, with the break time at $t_0=1.57\pm 0.03 days$. GRB 990510 is the most rapidly fading of the well-documented GRB afterglows. It is also the first observed example of broad-band break for a GRB optical counterpart. The optical spectral energy distribution, corrected for significant Galactic reddening, is well fitted by a single power-law with $\nu^{-0.61\pm 0.12}$. However, when the $B$-band point is dropped from the fit, the power-law becomes $\nu^{-0.46\pm 0.08}$, indicating a possible deviation from the power-law in the spectrum, either intrinsic or due to additional extinction near the source or from an intervening galaxy at $z=1.62$. Broad-band break behavior broadly similar to that observed in GRB 990510 has been predicted in some jet models of GRB afterglows, thus supporting the idea that the GRB energy is beamed, at least in some cases.Comment: submitted to the ApJ Letters, 13 pages, 5 tables, 3 figures; additional data available at ftp://cfa-ftp.harvard.edu/pub/kstanek/GRB990510/ and through WWW at http://cfa-www.harvard.edu/cfa/oir/Research/GRB

Cluster AgeS Experiment (CASE): Dwarf Novae and a Probable Microlensing Event in the Globular Cluster M22

We report the identification of a new cataclysmic variable (denoted as CV2) and a probable microlensing event in the field of the globular cluster M22. Two outbursts were observed for CV2. During one of them superhumps with P_sh=0.08875 d were present in the light curve. CV2 has an X-ray counterpart detected by XMM-Newton. A very likely microlensing event at a radius of 2.3 arcmin from the cluster center was detected. It had an amplitude of Delta_V=0.75 mag and a characteristic time of 15.9 days. Based on model considerations we show that the most likely configuration has the source in the Galactic bulge with the lens in the cluster. Two outbursts were observed for the already known dwarf nova CV1.Comment: 12 pages, 8 figures, accepted for publication in Acta Astronomic