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Optical flares and flaring oscillations on the M-type eclipsing binary CU Cancri
In this paper, we report on the discovery of an optical flare observedin the R band from the red-dwarf eclipsing binary CU Cancri, whosecomponent stars are at the upper boundary of full convection(M1= 0.43 M&sun; and M2= 0.4M&sun;, where M&sun; is the solar mass). Theamplitude of the flare is the largest among those detected in the R band(˜0.52 mag) and the duration time is about 73 min. Like flaresobserved on the Sun, quasi-periodic oscillations were seen during andafter the flare. Three more R-band flares were found by follow-upmonitoring. In total, this binary was monitored photometrically by usingan R filter for 79.9 h, which has revealed an R-band flare rate of about0.05 flares per hour. Together with other strong chromospheric andcoronal activities (i.e. very strong Hα andHβ emission features and an extreme ultraviolet andX-ray source), these detections indicate that it has very strongmagnetic activity. Therefore, the apparent faintness (˜1.4 mag inthe V band) of CU Cnc, compared with other single red dwarfs of the samemass, can be plausibly explained by the high coverage of dark spots.
| FR Cnc revisited: photometry, polarimetry and spectroscopy
This paper is part of a multiwavelength study aimed at usingcomplementary photometric, polarimetric and spectroscopic data toachieve an understanding of the activity process in late-type stars.Here, we present the study of FR Cnc, a young, active and spotted star.We performed analysis of All Sky Automated Survey 3 (ASAS-3) data forthe years 2002-08 and amended the value of the rotational period to be0.826518 d. The amplitude of photometric variations decreased abruptlyin the year 2005, while the mean brightness remained the same, which wasinterpreted as a quick redistribution of spots. BVRC andIC broad-band photometric calibration was performed for 166stars in FR Cnc vicinity.The photometry at Terskol Observatory shows two brightening episodes,one of which occurred at the same phase as the flare of 2006 November23. Polarimetric BVR observations indicate the probable presence of asupplementary source of polarization. We monitored FR Cncspectroscopically during the years 2004-08. We concluded that the radialvelocity changes cannot be explained by the binary nature of FR Cnc. Wedetermined the spectral type of FR Cnc as K7V. Calculated galacticspace-velocity components (U, V, W) indicate that FR Cnc belongs to theyoung disc population and might also belong to the IC 2391 moving group.Based on Li Iλ6707.8 measurement, we estimated the age of FR Cncto be between 10 and 120 Myr. Doppler tomography was applied to create astarspot image of FR Cnc. We optimized the goodness of fit to thedeconvolved profiles for axial inclination, equivalent width and v sin i, finding v sin i=46.2 km s-1 and i= 55°. We alsogenerated a synthetic V-band light curve based on Doppler imaging thatmakes simultaneous use of spectroscopic and photometric data. Thissynthetic light curve displays the same morphology and amplitude as theobserved one.The starspot distribution of FR Cnc is also of interest since it is oneof the latest spectral types to have been imaged. No polar spot wasdetected on FR Cnc. FWHM of the arc comparison lines. 2.2-m telescopeat the German-Spanish Astronomical Observatory (CAHA, Almería,Spain). 2.0-m Himalayan Chandra Telescope at the Indian AstronomicalObservatory (Mt Saraswati, Hanle, India). Nordic Optical Telescope (NOT)at the Observatorio del Roque de los Muchachos (La Palma, Spain). TheFibre Optics Cassegrain Echelle Spectrograph (FOCES). Himalaya FaintObject Spectrograph and Camera (HFOSC). The high-resolution Fibre-fedEchelle Spectrograph (FIES).
| Effect of magnetic activity saturation in chromospheric flux-flux relationships
We present a homogeneous study of chromospheric and coronal flux-fluxrelationships using a sample of 298 late-type dwarf active stars withspectral types F to M. The chromospheric lines were observedsimultaneously in each star to avoid spread as a result of long-termvariability. Unlike other works, we subtract the basal chromosphericcontribution in all the spectral lines studied. For the first time, wequantify the departure of dMe stars from the general relations. We showthat dK and dKe stars also deviate from the general trend. Studying theflux-colour diagrams, we demonstrate that the stars deviating from thegeneral relations are those with saturated X-ray emission and we showthat these stars also present saturation in the H? line. Usingseveral age spectral indicators, we show that these are younger starsthan those following the general relationships. The non-universality offlux-flux relationships found in this work should be taken into accountwhen converting between fluxes in different chromospheric activityindicators.
| XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources
The 18,806 ROSAT All Sky Survey Bright Source Catalog (RASS/BSC) X-raysources are quantitatively cross-associated with near-infrared (NIR)sources from the Two Micron All Sky Survey Point Source Catalog(2MASS/PSC). An association catalog is presented, listing the mostlikely counterpart for each RASS/BSC source, the probability Pid that the NIR source and X-ray source are uniquelyassociated, and the probability P no-id that none of the2MASS/PSC sources are associated with the X-ray source. The catalogincludes 3853 high quality (P id>0.98) X-ray-NIR matches,2280 medium quality (0.98 >= P id>0.9) matches, and4153 low quality (0.9 >= P id>0.5) matches. Of the highquality matches, 1418 are associations that are not listed in the SIMBADdatabase, and for which no high quality match with a USNO-A2 opticalsource was presented for the RASS/BSC source in previous work. Thepresent work offers a significant number of new associations withRASS/BSC objects that will require optical/NIR spectroscopy forclassification. For example, of the 6133 P id>0.92MASS/PSC counterparts presented in the association catalog, 2411 haveno classification listed in the SIMBAD database. These 2MASS/PSC sourceswill likely include scientifically useful examples of known sourceclasses of X-ray emitters (white dwarfs, coronally active stars, activegalactic nuclei), but may also contain previously unknown sourceclasses. It is determined that all coronally active stars in theRASS/BSC should have a counterpart in the 2MASS/PSC, and that the uniqueassociation of these RASS/BSC sources with their NIR counterparts thusis confusion limited.
| A Photometric Survey for Variables and Transits in the Field of Praesepe with the Kilodegree Extremely Little Telescope
The Kilodegree Extremely Little Telescope (KELT) project is a smallaperture, wide-angle search for planetary transits of solar-type stars.In this paper, we present the results of a commissioning campaign withthe KELT telescope to observe the open cluster Praesepe for 34 nights inearly 2005. Light curves were obtained for 69,337 stars, out of which weidentify 58 long-period variables and 152 periodic variables. Sixteen ofthese are previously known as variable, yielding 194 newly discoveredvariable stars for which we provide properties and light curves. We alsosearched for planetary-like transits, finding four transit candidates.Follow-up observations indicate that two of the candidates areastrophysical false positives, with two candidates remaining aspotential planetary transits.
| Detection of a Large Flare in FR Cnc (=1RXS J083230.9+154940)
We report detection of an optical flare in the BY Draconis type star FRCnc. The flare duration is 41 min, the amplitude is in the B band 1.02m. It is the first flare reported for this object.
| Aryabhatta Research Institute of Observational Sciences: reincarnation of a 50 year old State Observatory of Nainital
The fifty year old State Observatory, well known as U.P. StateObservatory till the formation of Uttaranchal in November 2000, was reincarnated on March 22, 2004 as Aryabhatta Research Institute ofObservational Sciences with acronym ARIES, an autonomous institute,under the Department of Science & Technology, Government of India.The growth of academic and technical activities and new mandate of theInstitute are briefly described. In early 60's, the Institute was one ofthe 12 centres established by the Smithsonian AstrophysicalObservatory, USA, all over the globe but the only centre in India forimaging artificial earth satellites. Commensurating with its observingcapabilities, the Institute started a number of front-line researchprogrammes during the last decade, e.g., optical follow up observationsof GRB afterglows, radio and space borne astronomical resources,intra-night optical variability in active galactic nuclei as well asgravitational microlensing and milli-magnitude variations in the rapidlyoscillating peculiar A type stars. As a part of atmospheric studies,characterisation of aerosol at an altitude of about 2 km is going onsince 2002. ARIES has plans for establishing modern observing facilities equipped with latest backend instruments in the area of bothastrophysics and atmospheric science. Formation of ARIES, thereforeaugurs well for the overall development of astrophysics and atmosphericscience in India.
| Optical and X-Ray Studies of Chromospherically Active Stars: FR Cancri, HD 95559, and LO Pegasi
We present a multiwavelength study of three chromospherically activestars, namely, FR Cnc (BD +16°1753), HD 95559, and LO Peg (BD+22°4409), including newly obtained optical photometry andlow-resolution optical spectroscopy for FR Cnc, as well as archival IRand X-ray observations. The BVR photometry carried out from 2001 to 2004has found significant photometric variability to be present in all threestars. For FR Cnc, a photometric period of 0.8267+/-0.0004 days has beenestablished. The strong variation in the phase and amplitude of the FRCnc light curves when folded on this period implies the presence ofevolving and migrating spots or spot groups on its surface. Twoindependent spots with migration periods of 0.97 and 0.93 yr,respectively, are inferred. The photometry of HD 95559 suggests theformation of a spot (group) during the interval of our observations. Weinfer the existence of two independent spots or groups in thephotosphere of LO Peg, one of which has a migration period of 1.12 yr.The optical spectroscopy of FR Cnc carried out during 2002-2003 revealsthe presence of strong and variable Ca II H and K, Hβ, and Hαemission features indicative of a high level of chromospheric activity.The value of 5.3 for the ratio of the excess emission in Hα toHβ, EHα/EHβ, suggests that thechromospheric emission may arise from an extended off-limb region. Wehave searched for the presence of color excesses in the near-IR JHKbands of these stars using Two Micron All Sky Survey data, but none ofthem appear to have any significant color excess. We have also analyzedarchival X-ray observations of HD 95559 and LO Peg carried out with theROSAT observatory. The best-fit models to their X-ray spectra imply thepresence of two coronal plasma components of differing temperatures andwith subsolar metal abundances. The inferred emission measures andtemperatures of these systems are similar to those found for otheractive dwarf stars. The kinematics of FR Cnc suggest that it is a veryyoung (35-55 Myr) main-sequence star and a possible member of the IC2391 supercluster. LO Peg also has young disk-type kinematics and hasbeen previously suggested to be a member of the 100 Myr old LocalAssociation (Pleiades moving group). The kinematics of HD 95559 indicateit is a possible member of the 600 Myr old Hyades supercluster.
| New Photoelectric Photometry of the Young Star LO Pegasi
Not Available
| FR Cnc - A Young Spotted Star
Optical photometric and spectroscopic studies of the star FR Cnc = BD +16 1753 have been carried out during the years 2001 - 2002. The star isphotometrically variable with a mean period of 0d.8271 ± 0.0002.The rapid changes in the shape of light curve can be attributed to theformation and distribution of two groups of spots on the surface of thestar. The presence of strong CaII H, K and H emission lines in thespectra indicates high chromospheric activity in the star. Thekinematics of the star suggest that it belongs young population of diskstars.
| FR Cnc = BD +16 d 1753 - A Young Active Main-Sequence Star
Not Available
| Photometric Variability of Four Coronally Active Stars
We present photometric observations of four stars that are opticalcounterparts of soft X-ray/EUV sources, namely 1ES 0829+15.9,1ES0920-13.6, 2RE J110159+223509 and 1ES 1737+61.2. We have discoveredperiodic variability in two of the stars, viz., MCC 527 (1ES 0829+15.9;Period = 0d :828 0:0047) and HD 81032 (1ES 0920-13.6; Period = ~ 57:020:560 days). HD 95559 (2RE J110159+223509) is found to show a period of3d . HD 160934 (1ES1737+61.2) also shows photometric variability butneeds to be monitored further for finding its period. These stars mostlikely belong to the class of chromospherically active stars.
| Space Motions of Low-Mass Stars. III.
Radial velocity observations are presented for 149 stars taken from theMcCormick lists of dwarf K and M stars in a continuing program of radialvelocities of faint nearby stars. The data will serve to derive a totalstellar density of these kinds of stars in the solar neighborhood. Thesedata were obtained with the spectrometer of the Vilnius UniversityObservatory mounted on the 1.6 m Kuiper Telescope of the StewardObservatory.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Optical and X-Ray Characteristics of Stars Detected in the Einstein Slew Survey
We detect X-rays for the first time from 63 cool (types AM) stars. Thesestars are part of the 229 total stellar X-ray sources identified to datein the Einstein Slew Survey (hereafter Slew). We also list new X-raydata on one A star that may have a corona, five OB stars, and reportdiscoveries of two new T Tauri stars and two new cataclysmic variables.The stellar content of the Slew high-latitude subset (currently 93%identified for |b_II_| > 20^deg^) is 26%. This agrees well with theEinstein Extended Medium Sensitivity Survey (EMSS) stellar sample, whichonly considered high latitudes. Because of the large solid angle coveredby the Slew, and its shallow limiting flux, the sample will better probethe bright end of the stellar X-ray luminosity function (L_X_ >10^30^ ergs s^-1^). Presently (based on the 221 Slew stars with knownspectral types), the sample is dominated by late-type systems (coolerthan F; 68%). These include dMe's, BY Dra, RS CVn, and FK Comae systems.Based on the limiting magnitudes of catalogs searched to date, the Slewis assessed to be complete for spectral types earlier than K. Hence, Kand M systems will be prominent in the ~50 as yet unidentified stars. Wehave embarked on an extensive program to (1) confirm the X-rayidentifications with the optical counterparts; (2) search for Ca II Hand K and Balmer line emission as activity signatures; and (3) searchfor supporting evidence of magnetic activity by measuring rotationalvelocities and relating them to X-ray luminosity level. Of 64 proposedcoronal systems observed to date, we have confirmed 44 active stars,while in the remaining 20 we have been unable to find definitiveactivity. We have confirmed an additional 19 active stars from stellardatabase searches, and reclassified nine systems as having nonstellaroptical counterparts from optical follow-up identification work andextragalactic database searches. We discuss notable new discoveries.From the sample of single active F7-MS Slew stars with measured ν sini-values, we find a strong (99.9% confidence level) linear correlationof X-ray luminosity with ν sin i and with stellar radius (R).However, L_X_ is uncorrelated with angular rotation speed at the 99%level. For the combined Slew and EMSS single star F7-MS sample, we findthe same 99.9% ν sin i-L_X_ and R-L_X_ correlations. The L_X_-νsin i relation for the combined sample appears to flatten with respectto the quadratic behavior seen for optically selected stellar samples atrotational velocities in excess of ~16 km s^-1^. For the unevolvedsubset of the Slew single star sample, we also find a correlationbetween L_X_ and Rossby number (R_0_; more than 99% confidence). Aleast-squares fit gives L_X_ ~ R_0_^-0.4^, which is similarly flatterthan the quadratic dependence seen in optical samples. Using the stellarsurface X-ray flux F_X_ versus B - V diagram, we interpret these resultsas saturation of the stellar surface by active regions at F_X_/F_bol_ ~10^-3^.
| Photometry of dwarf K and M stars
An observational program using UBVRI photometry is presented for 688stars from among the dwarf K and M stars already found spectroscopicallyby Vyssotsky (1958). Of these, 211 have not been observedphotometrically. These observations were obtained over a period ofseveral years at the Kitt Peak National Observatory using a GaAsphotomultiplier with an 0.9 m reflector. Based on night-to-nightvariations in the measures of individual stars, the internal errors maybe estimated to be roughly 0.01 mag for the colors and 0.015 for the Vmagnitudes. The photometric parallaxes reported for each star werecomputed in the manner discussed by Weis (1986).
| The Einstein Slew Survey
A catalog of 819 sources detected in the Einstein IPC Slew Survey of theX-ray sky is presented; 313 of the sources were not previously known asX-ray sources. Typical count rates are 0.1 IPC count/s, roughlyequivalent to a flux of 3 x 10 exp -12 ergs/sq cm s. The sources havepositional uncertainties of 1.2 arcmin (90 percent confidence) radius,based on a subset of 452 sources identified with previously knownpointlike X-ray sources (i.e., extent less than 3 arcmin).Identifications based on a number of existing catalogs of X-ray andoptical objects are proposed for 637 of the sources, 78 percent of thesurvey (within a 3-arcmin error radius) including 133 identifications ofnew X-ray sources. A public identification data base for the Slew Surveysources will be maintained at CfA, and contributions to this data baseare invited.
| Photovisual magnitudes of 418 dwarf M stars and 34 parallax stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1956AJ.....61..219S&db_key=AST
| Dwarf M stars found spectrophotometrically .
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1956AJ.....61..201V&db_key=AST
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