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The 78th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 1706 variable stars recently designated in the system ofthe General Catalogue of Variable Stars.
| Mass loss and orbital period decrease in detached chromospherically active binaries
The secular evolution of the orbital angular momentum (OAM), thesystemic mass (M=M1+M2) and the orbital period of114 chromospherically active binaries (CABs) were investigated afterdetermining the kinematical ages of the subsamples which were setaccording to OAM bins. OAMs, systemic masses and orbital periods wereshown to be decreasing by the kinematical ages. The first-orderdecreasing rates of OAM, systemic mass and orbital period have beendetermined as per systemic OAM, per systemic mass and per orbitalperiod, respectively, from the kinematical ages. The ratio of d logJ/dlogM= 2.68, which were derived from the kinematics of the presentsample, implies that there must be a mechanism which amplifies theangular momentum loss (AML) times in comparison to isotropic AML ofhypothetical isotropic wind from the components. It has been shown thatsimple isotropic mass loss from the surface of a component or bothcomponents would increase the orbital period.
| 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.
| Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution
The kinematics of 237 chromospherically active binaries (CABs) werestudied. The sample is heterogeneous with different orbits andphysically different components from F to M spectral-type main-sequencestars to G and K giants and supergiants. The computed U, V, W spacevelocities indicate that the sample is also heterogeneous in velocityspace. That is, both kinematically younger and older systems exist amongthe non-evolved main sequence and the evolved binaries containing giantsand subgiants. The kinematically young (0.95 Gyr) subsample (N= 95),which is formed according to the kinematical criteria of moving groups,was compared with the rest (N= 142) of the sample (3.86 Gyr) toinvestigate any observational clues of binary evolution. Comparing theorbital period histograms between the younger and older subsamples,evidence was found supporting the finding of Demircan that the CABs losemass (and angular momentum) and evolve towards shorter orbital periods.The evidence of mass loss is noticeable on the histograms of the totalmass (Mh+Mc), which is compared between theyounger (only N= 53 systems available) and older subsamples (only N= 66systems available). The orbital period decrease during binary evolutionis found to be clearly indicated by the kinematical ages of 6.69, 5.19and 3.02 Gyr which were found in the subsamples according to the periodranges of logP<= 0.8, 0.8 < logP<= 1.7 and 1.7 < logP<=3, respectively, among the binaries in the older subsample.
| The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
| 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.
| A complete sample of Seyfert galaxies selected at 0.25 keV
We have used the ROSAT Bright Source Catalogue to extract a completesample of sources selected in the band from 0.1-0.4keV. This0.25keV-selected sample is composed of 54 Seyfert galaxies, 25 BLLacertae objects, 4 clusters and 27 Galactic stars or binaries.Seyfert-type galaxies with `ultrasoft' X-ray spectra can very often beclassed optically as narrow-line Seyfert 1s (NLS1s). Such objects arereadily detected in 0.25keV surveys; the sample reported here contains20 NLS1s, corresponding to a 40 per cent fraction of the Seyferts.Optical spectra of the Seyfert galaxies were gathered for correlativeanalysis, which confirmed the well-known relations between X-ray slopeand optical spectral properties (e.g. [Oiii]/Hβ ratio; Feiistrength, Hβ width). The various intercorrelations are most likelydriven, fundamentally, by the shape of the photoionizing continuum inSeyfert nuclei. We argue that a steep X-ray spectrum is a betterindicator of an `extreme' set of physical properties in Seyfert galaxiesthan is the narrowness of the optical Hβ line. The correlationstudies were also used to isolate a number of Seyfert galaxies withapparently `anomalous' properties. Of particular interest are the sixobjects with relatively weak permitted line emission (Hβ and Feii)and weak optical continua. Such objects are rare in most surveys, buttwo of these (IC 3599 and NGC 5905) are known to be transient activegalactic nuclei in which the X-ray flux has faded by factors ~100. Ifthe other four objects also turn out to be transient, this woulddemonstrate that 0.25keV surveys provide an efficient way of finding aninteresting class of object. Finally, the luminosity function of the0.25keV-selected Seyfert galaxies was determined and broken down intosubsamples to investigate the relative space densities of Seyferts whenseparated on the basis of either X-ray slope or Hβ linewidth.
| Chromospherically Active Stars. XVIII. Sorting Out the Variability of HD 95559 and Gliese 410=DS Leonis
We have obtained spectroscopy and photometry of HD 95559 and photometryof Gliese 410=DS Leonis. HD 95559 consists of a pair of essentiallyidentical K1 V stars, whose orbital period we refine to1.52599775+/-0.00000104 days. The system is photometrically variablewith a mean period of 1.5264+/-0.0003 days. Despite minimum massesgreater than 0.8 Msolar for each component, a search foreclipses proved negative. The lithium abundances of the components of HD95559 indicate that the system is younger than the Hyades cluster, andits components may even have just arrived on the zero-age main sequence.Gl 410=DS Leo is also a photometric variable, but we conclude that thephotometric period originally ascribed to this star is an alias of theperiod for HD 95559. We find periods of 13.99 and 15.71 days for thefirst and second seasons of observation, respectively. Both HD 95559 andGl 410 are BY Draconis variables, with variability resulting from therotational modulation of starspots. We also find HR 4269, the check starfor our photometry of HD 95559 and Gl 410, to be a variable K4 III witha photometric period of 26.4 days in the first season of observation andperiods of 13.96 and 83 days in the second. We suggest that itsvariability mechanism is radial pulsation, the same as that for M giantsemiregular variables.
| The Vienna-KPNO search for Doppler-imaging candidate stars. I. A catalog of stellar-activity indicators for 1058 late-type Hipparcos stars
We present the results from a spectroscopic Ca ii H&K survey of 1058late-type stars selected from a color-limited subsample of the Hipparcoscatalog. Out of these 1058 stars, 371 stars were found to showsignificant H&K emission, most of them previously unknown; 23% withstrong emission, 36% with moderate emission, and 41% with weak emission.These spectra are used to determine absolute H&K emission-linefluxes, radial velocities, and equivalent widths of theluminosity-sensitive Sr ii line at 4077 Ä. Red-wavelengthspectroscopic and Strömgren y photometric follow-up observations ofthe 371 stars with H&K emission are used to additionally determinethe absolute Hα -core flux, the lithium abundance from the Li i6708 Å equivalent width, the rotational velocity vsin i, theradial velocity, and the light variations and its periodicity. Thelatter is interpreted as the stellar rotation period due to aninhomogeneous surface brightness distribution. 156 stars were found withphotometric periods between 0.29 and 64 days, 11 additional systemsshowed quasi-periodic variations possibly in excess of ~50 days. Further54 stars had variations but no unique period was found, and four starswere essentially constant. Altogether, 170 new variable stars werediscovered. Additionally, we found 17 new SB1 (plus 16 new candidates)and 19 new SB2 systems, as well as one definite and two possible new SB3systems. Finally, we present a list of 21 stars that we think are mostsuitable candidates for a detailed study with the Doppler-imagingtechnique. Tables A1--A3 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The ROSAT Bright Survey: II. Catalogue of all high-galactic latitude RASS sources with PSPC countrate CR > 0.2 s-1
We present a summary of an identification program of the more than 2000X-ray sources detected during the ROSAT All-Sky Survey (Voges et al.1999) at high galactic latitude, |b| > 30degr , with countrate above0.2 s-1. This program, termed the ROSAT Bright Survey RBS, isto more than 99.5% complete. A sub-sample of 931 sources with countrateabove 0.2 s-1 in the hard spectral band between 0.5 and 2.0keV is to 100% identified. The total survey area comprises 20391deg2 at a flux limit of 2.4 x 10-12 ergcm-2 s-1 in the 0.5 - 2.0 keV band. About 1500sources of the complete sample could be identified by correlating theRBS with SIMBAD and the NED. The remaining ~ 500 sources were identifiedby low-resolution optical spectroscopy and CCD imaging utilizingtelescopes at La Silla, Calar Alto, Zelenchukskaya and Mauna Kea. Apartfrom completely untouched sources, catalogued clusters and galaxieswithout published redshift as well as catalogued galaxies with unusualhigh X-ray luminosity were included in the spectroscopic identificationprogram. Details of the observations with an on-line presentation of thefinding charts and the optical spectra will be published separately.Here we summarize our identifications in a table which contains opticaland X-ray information for each source. As a result we present the mostmassive complete sample of X-ray selected AGNs with a total of 669members and a well populated X-ray selected sample of 302 clusters ofgalaxies with redshifts up to 0.70. Three fields studied by us remainwithout optical counterpart (RBS0378, RBS1223, RBS1556). While the firstis a possible X-ray transient, the two latter are isolated neutron starcandidates (Motch et al. 1999, Schwope et al. 1999).
| The Second Extreme Ultraviolet Explorer Right Angle Program Catalog
We present the detection of 235 extreme ultraviolet sources, of which169 are new detections, using the Extreme Ultraviolet Explorer's (EUVE)Right Angle Program (RAP) data. This catalog includes observations sincethe first EUVE RAP catalog (1994 January) and covers 17% of the sky. TheEUVE RAP uses the all-sky survey telescopes (also known as``scanners''), mounted at right angles to the Deep Survey andspectrometer instruments, to obtain photometric data in four wavelengthbands centered at ~100 Å (Lexan/B), ~200 Å (Al/Ti/C), ~400Å (Ti/Sb/Al), and ~550 Å (Sn/SiO). This allows the RAP toaccumulate data serendipitously during pointed spectroscopicobservations. The long exposure times possible with RAP observationsprovide much greater sensitivity than the all-sky survey. We presentEUVE source count rates and probable source identifications from theavailable catalogs and literature. The source distribution is similar toprevious extreme ultraviolet (EUV) catalogs with 2% early-type stars,45% late-type stars, 8% white dwarfs, 6% extragalactic, 24% with no firmclassification, and 15% with no optical identification. We also present36 detections of early-type stars that are probably the result ofnon-EUV radiation. We have detected stellar flares from approximately 12sources, including: EUVE J0008+208, M4 star G32-6 (EUVE J0016+198), anew source EUVE J0202+105, EUVE J0213+368, RS CVn V711 Tau (EUVEJ0336+005), BY Draconis type variable V837 Tau (EUVE J0336+259), the newK5 binary EUVE J0725-004, EUVE J1147+050, EUVE J1148-374, EUVE J1334-083(EQ Vir), EUVE J1438-432 (WT 486/487), EUVE J1808+297, and the M5.5estar G208-45 (EUVE J1953+444). We present sample light curves for thebrighter sources.
| Rotational Velocities of Late-Type Stars
A calibration based on the results of Gray has been used to determineprojected rotational velocities for 133 bright stars with spectral typesof F, G, or K, most of which appear in {\it The Bright Star Catalogue}.The vast majority have {\it v} sin {\it i} $\leq$ 10 km s$^{-1}$ and,thus, are slow rotators. With the new calibration, projected rotationalvelocities have been determined for a sample of 111 late-type stars,most of which are chromospherically active. Some of the stars have hadtheir rotational velocities measured for the first time. (SECTION:Stars)
| A Spectroscopic Survey of Late F--K Eclipsing Binaries
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..106..133P&db_key=AST
| New Extreme Ultraviolet-Selected Active Binaries from the ROSAT Wide Field Camera all Sky Survey
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995MNRAS.276..397J&db_key=AST
| Optical identification of EUV sources from the ROSAT Wide Field Camera all-sky survey
Optical identifications for 195 EUV sources located in the ROSAT WideField Camera all-sky survey are presented. We list 69 previously unknownEUV-emitting white dwarfs, 114 active stars, 7 new magnetic cataclysmicvariables and 5 active galaxies. Several of the white dwarfs haveresolved M-type companions, while five are unresolved white dwarf/M-starpairs. Finding charts are given for the optical counterparts.
| The ROSAT Wide Field Camera all-sky survey of extreme-ultraviolet sources - II. The 2RE Source Catalogue
During 1990-1991 the Wide Field Camera (WFC) on the ROSAT satelliteperformed the first all-sky survey at EUV wavelengths. The survey wasconducted in two `colours' using broad-band filters to define wavebandscovering the ranges 60-140 A and 112-200 A. It was fully imaging, witheffective spatial resolution of about 3 arcmin FWHM, and point sourcelocation accuracy of typically better than 1 arcmin. From an initialanalysis, Pounds et al. published the WFC Bright Source Catalogue (BSC)of 383 sources. In this paper we report results from reprocessing of thecomplete survey database; the resulting list of sources is the `2RE'Catalogue. It contains 479 sources, of which 387 are detected in bothsurvey wavebands, a significant advance on the BSC (80 per cent versus60 per cent). Improvements over the original BSC include: (i) betterrejection of poor aspect periods, and smaller random errors in theaspect reconstruction; (ii) improved background screening; (iii)improved methods for source detection; (iv) inclusion of atime-variability test for each source; (v) more extensive investigationof the survey sensitivity. We define the catalogue selection criteria,and present the catalogue contents in terms of tables and sky maps. Wealso discuss the sky coverage, source number-flux relations, opticalidentifications and source variability.
| Is Gliese 410 or BD +23 2297 the Variable Star?
Not Available
| Observations of active chromosphere stars
It is pointed out that spectroscopic signatures of stellar chromosphericactivity are readily observable. The present study is concerned with newphotometric and spectroscopic observations of active-chromosphere RSCVn, BY Dra, and FK Com stars. Attention is given to the first resultsof a synoptic monitoring program of many active chromosphere stars.During the time from 1980 to 1982, photometric and spectroscopicobservations of 10 known or suspected active-chromosphere objects weremade. The results regarding the individual stars are discussed. Sevenstars observed with the International Ultraviolet Explorer (IUE) are allspectroscopic binaries.
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Osservazione e dati astrometrici
| Costellazione: | Leone |
| Ascensione retta: | 11h02m02.27s |
| Declinazione: | +22°35'45.5" |
| Magnitudine apparente: | 8.968 |
| Distanza: | 54.259 parsec |
| Moto proprio RA: | -141.4 |
| Moto proprio Dec: | 5.3 |
| B-T magnitude: | 10.027 |
| V-T magnitude: | 9.056 |
Cataloghi e designazioni:
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