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Chandra Observations of Coronal Emission from the Early G Supergiants α and β Aquarii
We report Chandra detections of coronal X-rays from the early Gsupergiants α Aquarii (HD 209750: G2 Ib) and β Aquarii (HD204867: G0 Ib). Previous ROSAT observations of these archetypical``hybrid chromosphere'' stars were inconclusive, in the case of αAqr owing to a 38' mispointing, and for β Aqr because of a smallpositional discrepancy of the apparent source. The Chandra HighResolution Camera (HRC-I), with its superior spatial resolution andsensitivity, has obtained a positive detection of α Aqr andrecovered faint emission at the location of β Aqr, now wellseparated from the stronger source to the southeast that dominated theearlier ROSAT image. The coronal LX/LC IV luminosity ratiosof both supergiants are extremely depressed relative to early Gmain-sequence stars, continuing the ``X-ray deficiency syndrome''originally identified in late F/early G luminosity class III giants ofthe Hertzsprung gap.
| X-Rays from Hybrid Stars
The late-type giants and supergiants of the ``hybrid chromosphere''class display signatures of cool (T<~2×104 K) windstogether with hot emission lines from species like C IV(T~105 K). A survey of such stars by Reimers et al. usingROSAT reported numerous X-ray detections (T~106 K),strengthening the (then heretical) idea that hot coronae and cool windscan coexist in luminous giants. However, several of the candidatesources were offset from the predicted stellar coordinates, calling intoquestion the identifications. In an effort to secure better knowledge ofthe X-ray luminosities of the hybrids, the ROSAT fields from the Reimerset al. survey were reexamined, exploiting the USNO-A2.0 astrometriccatalog to register the pointings to a few arcseconds accuracy. On thebasis of positional mismatches, at least two of the previously reporteddetections of key hybrid stars-γ Dra (K5 III) and β Aqr (G0Ib)-must be rejected. The new X-ray upper limits for these stars,combined with the remaining candidate detections (and nondetections)from the original survey, place the hybrids into the same ``X-raydeficient'' category as the ``noncoronal'' red giants like Arcturus(α Boo: K1.5 III) and Aldebaran (α Tau: K5 III). A few ofthe hybrid X-ray sources are exceptional, however. The archetype αTrA (K2 II-III), in particular, is securely detected in terms ofpositional coincidence, but its anomalous, contradictory coronalproperties suggest that an unseen companion-a young hyperactive Gdwarf-might dominate the X-ray emission.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| J - K DENIS photometry of a VLTI-selected sample of bright southern stars
We present a photometric survey of bright southern stars carried outusing the DENIS instrument equipped with attenuating filters. Theobservations were carried out not using the survey mode of DENIS, butwith individual target pointings. This project was stimulated by theneed to obtain near-infrared photometry of stars to be used in earlycommissioning observations of the ESO Very Large TelescopeInterferometer, and in particular to establish a network of brightcalibrator sources.We stress that near-infrared photometry is peculiarly lacking for manybright stars. These stars are saturated in 2MASS as well as in regularDENIS observations. The only other observations available for brightinfrared stars are those of the Two Micron Sky Survey dating from overthirty years ago. These were restricted to declinations above≈-30°, and thus cover only about half of the sky accessible fromthe VLTI site.We note that the final 2MASS data release includes photometry of brightstars, obtained by means of point-spread function fitting. However, thismethod only achieves about 30% accuracy, which is not sufficient formost applications.In this work, we present photometry for over 600 stars, each with atleast one and up to eight measurements, in the J and K filters. Typicalaccuracy is at the level of 0\fm05 and 0\fm04 in the J and K_s bands,respectively.Based on observations collected at the European Southern Observatory, LaSilla.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/413/1037
| A catalogue of calibrator stars for long baseline stellar interferometry
Long baseline stellar interferometry shares with other techniques theneed for calibrator stars in order to correct for instrumental andatmospheric effects. We present a catalogue of 374 stars carefullyselected to be used for that purpose in the near infrared. Owing toseveral convergent criteria with the work of Cohen et al.(\cite{cohen99}), this catalogue is in essence a subset of theirself-consistent all-sky network of spectro-photometric calibrator stars.For every star, we provide the angular limb-darkened diameter, uniformdisc angular diameters in the J, H and K bands, the Johnson photometryand other useful parameters. Most stars are type III giants withspectral types K or M0, magnitudes V=3-7 and K=0-3. Their angularlimb-darkened diameters range from 1 to 3 mas with a median uncertaintyas low as 1.2%. The median distance from a given point on the sky to theclosest reference is 5.2degr , whereas this distance never exceeds16.4degr for any celestial location. The catalogue is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/183
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/386/492, and from theauthors on CD-Rom.
| On the Variability of K5-M Stars
I investigate the Hipparcos Satellite photometry of K5-M stars to seethe pattern of activity of these stars. A few stars for which furtherstudy is desirable are identified.
| Spectral Irradiance Calibration in the Infrared. X. A Self-Consistent Radiometric All-Sky Network of Absolutely Calibrated Stellar Spectra
We start from our six absolutely calibrated continuous stellar spectrafrom 1.2 to 35 μm for K0, K1.5, K3, K5, and M0 giants. These wereconstructed as far as possible from actual observed spectral fragmentstaken from the ground, the Kuiper Airborne Observatory, and the IRAS LowResolution Spectrometer, and all have a common calibration pedigree.From these we spawn 422 calibrated ``spectral templates'' for stars withspectral types in the ranges G9.5-K3.5 III and K4.5-M0.5 III. Wenormalize each template by photometry for the individual stars usingpublished and/or newly secured near- and mid-infrared photometryobtained through fully characterized, absolutely calibrated,combinations of filter passband, detector radiance response, and meanterrestrial atmospheric transmission. These templates continue ourongoing effort to provide an all-sky network of absolutely calibrated,spectrally continuous, stellar standards for general infrared usage, allwith a common, traceable calibration heritage. The wavelength coverageis ideal for calibration of many existing and proposed ground-based,airborne, and satellite sensors, particularly low- tomoderate-resolution spectrometers. We analyze the statistics of probableuncertainties, in the normalization of these templates to actualphotometry, that quantify the confidence with which we can assert thatthese templates truly represent the individual stars. Each calibratedtemplate provides an angular diameter for that star. These radiometricangular diameters compare very favorably with those directly observedacross the range from 1.6 to 21 mas.
| The ROSAT all-sky survey catalogue of optically bright late-type giants and supergiants
We present X-ray data for all late-type (A, F, G, K, M) giants andsupergiants (luminosity classes I to III-IV) listed in the Bright StarCatalogue that have been detected in the ROSAT all-sky survey.Altogether, our catalogue contains 450 entries of X-ray emitting evolvedlate-type stars, which corresponds to an average detection rate of about11.7 percent. The selection of the sample stars, the data analysis, thecriteria for an accepted match between star and X-ray source, and thedetermination of X-ray fluxes are described. Catalogue only available atCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| On the X-ray emission from M-type giants
We have searched for X-ray emission from M-type giants and supergiantslisted in the Bright Star Catalogue (BSC) in the data of the ROSATall-sky survey (RASS). These stars lie to the far right of the X-raydividing line and are thus not expected to be X-ray sources. Any X-raydetection would therefore violate the common paradigm of X-ray darkM-type giants beyond the X-ray dividing line. We found 11 BSC M-typegiants and supergiants to coincide with RASS X-ray sources. While for 4stars the X-ray emission is very likely related to their cataclysmic orsymbiotic nature or can be attributed to a visual G-type companion, theother 7 stars are candidates for intrinsic X-ray emission. Of theseobjects, 3 have a rather large offset between optical and X-rayposition, so their proper identification with late-type giants is atleast questionable. For the remaining four stars, we obtained opticallow-dispersion spectra in order to search for emission lines indicativeof a possible symbiotic nature. None of these stars shows any brightemission lines, so they are probably quite normal M-type giants. Wediscuss possible origins of X-ray emission in these stars and theimportance of evolutionary aspects. Based on observations by the ROSATand Calar Alto Observatories
| Advances in Solar-Stellar Astrophysics
The discovery on stars of coronae and of X-ray emission from flares inthe 1970's opened up the investigation of stellar activity.Solar-stellar astrophysics has now become a two-way street. The richdetail of the Sun provides a close-up view of physical phenomena, whilethe stellar observations provide a way to, in effect, vary the otherwisefixed solar parameters. In this way we can study the evolution of theSun, the dependence of activity on rotation, and the degree of autonomybetween magnetic fields and such fundamental parameters as mass and age.We present an overview of the Sun as a star, stellar coronae along themain sequence, the dividing line for evolved stars, rotation-activityrelations, activity cycles, flux-flux relations, basal acoustic heating,evidence for coronal heating by microflaring, and a few facts aboutflares. (SECTION: Invited Review)
| HR 4289 - an X-ray luminous galaxy close to the bright star.
Using new optical, UV and X-ray observations we show that the K5 IIIstar HR 4289, formerly believed to be the only ROSAT All-Sky surveydetection to the right of the coronal diving line, should not beidentified with the X-ray source. Pointed ROSAT PSPC observationsdemonstrate that the X-ray source is slightly extended, and locate theX-ray source 30" northwest of HR 4289 at the position of a hithertounknown 15nag galaxy. The X-ray spectrum can well be fitted with aRaymond-Smith model for a thermal plasma at 6(+/-2)x10^6^K and ahydrogen column density of N_H_=3(+/-2)x10^21^cm^-2^. At a distance ofz=0.016 (96 h_50_^-1^Mpc), the galaxy has an X-ray luminosity ofL_x_=1.4x10^42^h_50_^-2^erg/s between 0.1 and 2.4keV.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Disappearance of coronal X-ray emission in stars with cool dense winds
X-ray observations have shown that stellar coronae seem to disappearabruptly across a 'dividing line' in the H-R diagram describing theevolution of intermediate-mass stars toward the red giant phase. Resultsfrom the Rosat all-sky survey are used here to show that the dividingline is not an artifact of poor sampling. Optical and UV observationshow that the dividing line in the H-R diagram coincides approximatelywith the onset of cool massive stellar winds, but it is shown here thatthese winds are not sufficiently dense for simple X-ray absorption to bethe cause of the disappearance of coronal emission. It is concluded thatthe dividing line represents a true evolutionary transition in thesestars at which the hot coronae are replaced by cool winds.
| The coronal dividing line in the ROSAT X-ray All-Sky Survey
Rosat All-Sky Survey soft X-ray observations of nearly 1000 brightsingle evolved stars of spectral types G, K, and M in the vicinity ofthe dividing line proposed by Linsky and Haisch (1979) are reported.Most observations consist of upper limits in the 0.1-2.0-keV banddistributed between 604 stellar targes of spectral type K3 or earlierand 264 stellar targets of spectral type K4 or later. Of the 65 Rosatdetections, only one involves an apparently single star of spectral typelater than K3: HR 4289 (K5 III). A clear dichotomy exists betweencoronal and noncoronal stars of luminosity classes II, III, and IV atapproximately spectral type Ke. The extremely low upper limit for thearchetypal 'noncoronal' red giant, Arcturus, less than 3 x 24 exp 25ergs/s achieved by Rosat during an 18.6-ks targeted observations byAyres et al. (1991) indicates a very steep decline at the coronaldividing line.
| Catalog of Indidual Radial Velocities, 0h-12h, Measured by Astronomers of the Mount Wilson Observatory
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJS...19..387A&db_key=AST
| Narrow-Band and Broad-Band Photometry of Red Stars. III. Southern Giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJ...161..199E&db_key=AST
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Dades d'Observació i Astrometria
| Constel·lació: | Crater |
| Ascensió Recta: | 11h00m11.60s |
| Declinació: | -14°05'00.0" |
| Magnitud Aparent: | 5.88 |
| Distancia: | 135.685 parsecs |
| Moviment propi RA: | -8.9 |
| Moviment propi Dec: | -31.7 |
| B-T magnitude: | 7.853 |
| V-T magnitude: | 6.037 |
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INHABITED SKY
