Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
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.
| The MODEST questions: Challenges and future directions in stellar cluster research
We present a review of some of the current major challenges in stellarcluster research, including young clusters, globular clusters, andgalactic nuclei. Topics considered include: primordial mass segregationand runaway mergers, expulsion of gas from clusters, the production ofstellar exotica seen in some clusters (e.g., blue stragglers and extremehorizontal-branch stars), binary populations within clusters, theblack-hole population within stellar clusters, the final parsec problem,stellar dynamics around a massive black hole, and stellar collisions.The Modest Questions posed here are the outcome of discussions whichtook place at the Modest-6A workshop held in Lund, Sweden, in December,2005. Modest-6A was organised as part of the activities of the ModestCollaboration (see www.manybody.org for further details).
| Stellar activity and the Konkoly Observatory: the beginnings
The early observational facts on stellar activity are discussed withspecial emphasis on L. Detre's interest in those results.
| GALEX high time-resolution ultraviolet observations of dMe flare events
Aims.We present near ultraviolet (NUV: 1750-2800 Å) and farultraviolet (FUV: 1350-1750 Å) light-curves for flares on 4 nearbydMe-type stars (GJ 3685A, CR Dra, AF Psc and SDSS J084425.9+513830.5)observed with the GALEX satellite. Methods: .Taking advantage ofthe time-tagged events recorded with the GALEX photon countingdetectors, we present high temporal resolution (<0.01 s) analysis ofthese UV flare data. Results: .A statistical analysis of 700 s ofpre-flare quiescence data for both CR Dra and SDSS J084425.9+513830.5failed to reveal the presence of significant micro-flare activity intime bins of 0.2, 1 and 10 s intervals. Using an appropriatedifferential emission measure for both the quiescent and flaring state,it is possible to reproduce the observed FUV:NUV flux ratios. A majordeterminant in reproducing this flux ratio is found to be the value ofplasma electron density during the flare. We also searched the countrate data recorded during each of the four flare events for periodicityassociated with magneto-hydrodynamic oscillations in the active regioncoronal loops. Significant oscillations were detected during the flareevents observed on all 4 stars, with periodicities found in the 30 to 40s range. Flare oscillations with this periodicity can be explained asacoustic waves in a coronal loop of length of ≈109 cm foran assumed plasma temperature of 5-20 × 106 K. Thissuggests a loop length for these M-dwarf flares of less than 1/10th ofthe stellar radii. We believe that this is the first detection ofnon-solar coronal loop flare oscillations observed at ultravioletwavelengths.
| The RS CVn binary HK Lacertae: long-term photometry from Sonneberg sky-patrol plates
Long-term photographic photometry of the active long-period RS CVnbinary HK Lac (HD 209813) was obtained from more than 2000 SonnebergSky-Patrol plates taken between 1956 and 1996. We achieve an internalaccuracy of 0.07 m. The correspondence with contemporaneoushigh-precision photoelectric photometry from automatic telescopes isstriking and successfully demonstrates the feasibility of our approach.Based on a Bayesian time series analysis, we improve the previouslypublished cycle period to 13.37± 0.08 years, and present evidenceof an additional period of 9.48± 0.13 years. This establishes themulti-periodicity of dynamo action in these overactive stars as comparedto the Sun. The already known 6.7-years cycle turns out to be anovertone of the dominating 13.4-years cycle. Our long-term photographicphotometry even allowed the detection of the star's mean rotationalperiod of 24.35 days.
| A Comparative Study of Flaring Loops in Active Stars
Dynamo activity in stars of different types is expected to generatemagnetic fields with different characteristics. As a result, adifferential study of the characteristics of magnetic loops in a broadsample of stars may yield information about dynamo systematics. In theabsence of direct imaging, certain physical parameters of a stellarmagnetic loop can be extracted if a flare occurs in that loop. In thispaper we employ a simple nonhydrodynamic approach introduced by Haisch,to analyze a homogeneous sample of all of the flares we could identifyin the EUVE DS database: a total of 134 flares that occurred on 44 starsranging in spectral type from F to M and in luminosity class from V toIII. All of the flare light curves that have been used in the presentstudy were obtained by a single instrument (EUVE DS). For each flare, wehave applied Haisch's simplified approach (HSA) in order to determineloop length, temperature, electron density, and magnetic field. For eachof our target stars, a literature survey has been performed to determinequantitatively the extent to which our results are consistent withindependent studies. The results obtained by HSA are found to be wellsupported by results obtained by other methods. Our survey suggeststhat, on the main sequence, short loops (with lengths<=0.5R*) may be found in stars of all classes, while thelargest loops (with lengths up to 2R*) appear to be confinedto M dwarfs. Based on EUVE data, the transition from small to largeloops on the main sequence appears to occur between spectral types K2and M0. We discuss the implications of this result for dynamo theories.
| On the Temperature-Emission Measure Distribution in Stellar Coronae
Strong peaks in the emission measure-temperature (EM-T ) distributionsin the coronae of some binary stars are associated with the presence ofhot (107 K), dense (up to 1013 cm -3)plasma. These peaks are very reminiscent of those predicted to arise inan impulsively heated solar corona. A coronal model comprised of manyimpulsively heated strands is adapted to stellar parameters. It is shownthat the properties of the EM-T distribution can be accounted for ingeneral terms provided the emission comes from many very small loops(length under 103 km) with intense magnetic fields (1 kG)distributed across part of the surface of the star. The heating requiresevents that generally dissipate between 1026 and 1028 ergs, which is in the range of solar microflares. This impliesthat such stars must be capable of generating regions of localizedintense magnetic fields.
| Tertiary companions to close spectroscopic binaries
We have surveyed a sample of 165 solar-type spectroscopic binaries (SB)with periods from 1 to 30 days for higher-order multiplicity. Asubsample of 62 targets were observed with the NACO adaptive opticssystem and 13 new physical tertiary companions were detected. Anadditional 12 new wide companions (5 still tentative) were found usingthe 2MASS all-sky survey. The binaries belong to 161 stellar systems; ofthese 64 are triple, 11 quadruple and 7 quintuple. After correction forincompleteness, the fraction of SBs with additional companions is foundto be 63% ± 5%. We find that this fraction is a strong functionof the SB period P, reaching 96% for P<3d and dropping to34% for P>12^d. Period distributions of SBs with and withouttertiaries are significantly different, but their mass ratiodistributions are identical. The statistical data on the multiplicity ofclose SBs presented in this paper indicates that the periods and massratios of SBs were established very early, but the periods of SB systemswith triples were further shortened by angular momentum exchange withcompanions.
| Starspot activity in late stars: Methods and results
Three types of methods for studying the surface inhomogeneities of coolstars and the results of their use on type BY Dra, RS CVn, FK Com, and TTau variables are discussed. The current relevance of traditionalphotometric methods and the advantages of the zonal spottedness modelare pointed out. Dependences of the maximum total areas, averagelatitudes, and temperatures of spots on the global parameters of thestars are given. Analogs of the solar cycle in the variations of theareas and latitudes of starspots are examined, as well as the effects ofdifferential rotation and active longitudes.
| 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.
| Speckle interferometry of nearby multiple stars. III.
Not Available
| 2MASS J05162881+2607387 is a Double-Lined Eclipsing Low-Mass Binary
The star known as 2MASS J05162881+2607387 (J0516) was discovered to bean eclipsing binary by Schuh et al. (2003, A&A, 410, 649). Assuming that the orbital period is the same as the eclipse period(1.29395 days), Schuh et al. suggested that J0516 consists of a K7Vstar and a brown dwarf. Schuh et al. also considered the possibilitythat the orbital period of J0156 was twice the eclipse period .
| The BY Dra star HD 77191 is a spectroscopic binary, but GQ Leo may not be
Not Available
| Astrometric orbits of SB^9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
| The case and fate of HD 75767 - neutron star or supernova?
We report the discovery of the nearby (d= 24 pc) HD 75767 as an eightbillion year old quadruple system consisting of a distant M dwarf pair,HD 75767 C-D, in orbit around the known short-period P= 10.25 dsingle-lined binary HD 75767 A-B, the primary of which is a solar-like Gstar. On the reasonable assumption of synchronous orbital rotation aswell as rotational and orbital coplanarity for the inner pair, we getMB= 0.96Msolar for the unseen HD 75767 B, that is,the case of a massive white dwarf. Upon future evolution, mass transfertowards HD 75767 B will render the MA= 0.96MsolarG-type primary, now a turnoff star, to become a helium white dwarf ofMA~ 0.33Msolar. Depending on the mass accretionrate, accretion efficiency and composition of the massive white dwarf,this in turn may result in a collapse of HD 75767 B with the formationof a millisecond pulsar, i.e. the creation of a low-mass binary pulsar(LMBP), or, instead, a Type Ia supernova explosion and the completedisruption of HD 75767 B. Irrespective of which scenario applies, wepoint to the importance of the distant M dwarfs as the likely agents forthe formation of the inner, short-period HD 75767 A-B pair, and hence apath that particularly avoids preceding phases of common envelopeevolution.
| Stellar activity cycles: observing the dynamo?
The enormous complexity of the atmospheric structure observed on the Sunmakes it very difficult to compare the Sun with ``solar-type stars''.Clearly, we need to identify parameters that can be observed on the Sunas well as on other stars which can be interpreted unambiguously. Themost widely accepted dynamo signature is the presence of an activitycycle, well documented for the Sun and for main-sequence stars due tothe Mount Wilson Ca II H&K project. Only recently have we detectedspatial information, differential rotation and possibly meridional flowson other stars and thereby adding another constraint for itsinterpretation within a dynamo theory. Again, the picture is notcomplete yet, despite that there is just a single main ingredient thatacts as the driving mechanism for activity in all atmospheric layers andthe convective envelope of a solar-type star: the dynamo-relatedmagnetic field. I stress the importance of mapping stellar surfaces asfingerprints of the underlying dynamo action over long periods of time.
| Statistical properties of exoplanets. IV. The period-eccentricity relations of exoplanets and of binary stars
A sample of spectroscopic binaries and a sample of single planetarysystems, both having main-sequence solar-type primary components, areselected in order to compare their eccentricities. The positions of theobjects in the (P.(1-e^2)3/2, e) plane is used to determineparts in the period eccentricity diagram that are not affected by tidalcircularization. The original eccentricities of binaries and planets arederived and compared. They seem to be weakly or not at all correlatedwith period in both samples, but two major differences are found: (1)The tidal circularization of planetary orbits is almost complete forperiods shorter than 5 days, but it is not visible whenP.(1-e^2)3/2 is longer than this limit. This suggests thatthe circularization occurs rapidly after the end of the migrationprocess and is probably simultaneous with the end of the formation ofthe planet. By contrast, we confirm that the circularization of thebinary orbits is a process still progressing a long time after theformation of the systems. (2) Beyond the circularization limit, theeccentricities of the orbits of the planets are significantly smallerthan those of binary orbits, and this discrepancy cannot be due to aselection effect. Moreover, the eccentricities of binaries with smallmass ratios are quite similar to those of all binaries with q<0.8.This suggests that the low eccentricities of exoplanet orbits are not aconsequence of low-mass secondaries in a universal process. Theseremarks are in favor of the idea that binaries and exoplanets are twodifferent classes of object from the point of view of their formation.
| 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
| The Hard Quiescent Spectrum of the Neutron Star X-Ray Transient EXO 1745-248 in the Globular Cluster Terzan 5
We present a Chandra observation of the globular cluster Terzan 5 duringtimes when the neutron star X-ray transient EXO 1745-248 located in thiscluster was in its quiescent state. We detected the quiescent systemwith a (0.5-10 keV) luminosity of ~2×1033 ergss-1. This is similar to several other neutron-star transientsobserved in their quiescent states. However, the quiescent X-rayspectrum of EXO 1745-248 was dominated by a hard power-law componentinstead of the soft component that usually dominates the quiescentemission of other neutron star X-ray transients. This soft componentcould not conclusively be detected in EXO 1745-248, and we conclude thatit contributed at most 10% of the quiescent flux in the energy range0.5-10 keV. EXO 1745-248 is only the second known neutron-star transientwhose quiescent spectrum is dominated by the hard component (SAXJ1808.4-3658 is the other one). We discuss possible explanations forthis unusual behavior of EXO 1745-248, its relationship to otherquiescent neutron-star systems, and the impact of our results onunderstanding quiescent X-ray binaries. We also discuss the implicationsof our results on the way that the low-luminosity X-ray sources inglobular clusters are classified.
| Spots, activity cycles, and differential rotation on cool stars
The first results are reported from a search for activity cycles instars similar to the sun based on modelling their spotting with analgorithm developed at the Crimean Astrophysical Observatory. Of themore than thirty program stars, 10 manifested a cyclical variation intheir central latitudes and total starspot area. The observed cycleshave durations of 4-15 years, i.e., analogous to the 11 year Schwabesunspot cycle. Most of the stars have a rough analog of the solarbutterfly pattern, with a reduction in the average latitude of the spotsas their area increases. A flip-flop effect during the epoch of themaximum average latitude is noted in a number of these objects (e.g.,the analog LQ Hya of the young sun or the RS CVn-type variable V711Tau), as well as a reduction in the photometric rotation period of astar as the spots drift toward the equator, an analog of thedifferential rotation effect in the sun. Unlike in the sun, the observedspot formation cycles do not correlate uniquely with other indicators ofactivity chromospheric emission in the CaII HK lines (Be Cet, EKDra, Dx Leo), H line emission (LQ Hya, VY Ari, EV Lac), or cyclicalflare activity (EV Lac). In V833 Tau, BY Dra, EK Dra, and VY Ari shortSchwabe cycles coexist with long cycles that are analogous to theGleissberg solar cycle, in which the spotted area can approach half theentire area of the star.
| Mg II chromospheric radiative loss rates in cool active and quiet stars
The Mg II k emission line is a good indicator of the level ofchromospheric activity in late-type stars. We investigate the dependenceof this activity indicator on fundamental stellar parameters. To thispurpose we use IUE observations of the Mg II k line in 225 late-typestars of luminosity classes I-V, with different levels of chromosphericactivity. We first re-analyse the relation between Mg II k lineluminosity and stellar absolute magnitude, performing linear fits to thepoints. The ratio of Mg II surface flux to total surface flux is foundto be independent of stellar luminosity for evolved stars and toincrease with decreasing luminosity for dwarfs. We also analyse the MgII k line surface flux-metallicity connection. The Mg II k emissionlevel turns out to be not dependent on metallicity. Finally, the Mg II kline surface flux-temperature relation is investigated by treatingseparately, for the first time, a large sample of very active and normalstars. The stellar surface fluxes in the k line of normal stars arefound to be strongly dependent on the temperature and slightly dependenton the gravity, thus confirming the validity of recently proposedmodels. In contrast, data relative to RS CVn binaries and BY Dra stars,which show very strong chromospheric activity, are not justified in theframework of a description based only on acoustic waves and uniformlydistributed magnetic flux tubes so that they require more detailedmodels.
| Archival light curves from the Bamberg Sky Patrol: CF Octantis, 1964-76
We use the archive of the Bamberg Sky Patrol to obtain light curves ofthe active K subgiant CF Octantis (HD 196818) for the interval 1964-76.Digitized images of the field near CF Oct were obtained with a flat-bedscanner. Aperture photometry was performed of photo-positives of theseimages. Using a transformation to second order in plate magnitude, andfirst order in B-V, for nine field stars for each plate, the Bmagnitudes of CF Oct were obtained for just over 350 plates. Theestimated precision of an individual determination of the B magnitude ofCF Oct is 0.05 mag. Analysis of the resulting data reveals the known 20d rotational variation of this star, and shows the evolution of thelight curves from year to year. We obtain light curves with good phasecoverage for 1964 to 1969 inclusive, partial light curves for 1970 and1976, and a few data points from 1971. The amplitude of variation rangesfrom ~0.2 to ~0.4 mag. There is evidence that the characteristicrotation period of the star in the 1960s was slightly less than thatmeasured from photoelectric photometry in the 1980s.
| X-ray astronomy of stellar coronae
X-ray emission from stars in the cool half of the Hertzsprung-Russelldiagram is generally attributed to the presence of a magnetic coronathat contains plasma at temperatures exceeding 1 million K. Coronae areubiquitous among these stars, yet many fundamental mechanisms operatingin their magnetic fields still elude an interpretation through adetailed physical description. Stellar X-ray astronomy is thereforecontributing toward a deeper understanding of the generation of magneticfields in magnetohydrodynamic dynamos, the release of energy in tenuousastrophysical plasmas through various plasma-physical processes, and theinteractions of high-energy radiation with the stellar environment.Stellar X-ray emission also provides important diagnostics to study thestructure and evolution of stellar magnetic fields from the first daysof a protostellar life to the latest stages of stellar evolution amonggiants and supergiants. The discipline of stellar coronal X-rayastronomy has now reached a level of sophistication that makes tests ofadvanced theories in stellar physics possible. This development is basedon the rapidly advancing instrumental possibilities that today allow usto obtain images with sub-arcsecond resolution and spectra withresolving powers exceeding 1000. High-resolution X-ray spectroscopy has,in fact, opened new windows into astrophysical sources, and has played afundamental role in coronal research.
| Statistics of multiple stars
The statistics of stellar systems of multiplicity three and higher isreviewed. They are frequent, 0.15-0.25 of all stellar systems. Some 700multiples are expected among the 3383 stars of spectral type F, G, and Kwithin 50 pc, while only 76 of them are actually known. Many (if notall) close binaries have distant tertiary components, indicating thatangular momentum exchange within multiple systems was probably criticalin forming short-period binaries. The ratio of outer to inner periods inthe best-studied nearby multiples and in low-mass pre-main sequencemultiples does not exceed 104 at the formation epoch; largerratios are produced by subsequent orbital evolution. All multiples withwell-defined orbits are dynamically stable, the eccentricities of outerorbits obey the empirical stability limit P[out](1 - e[out])3/P[in] >5 that is more strict than current theoretical limits. Relativeorientation of orbits in triple stars shows some degree of alignment,especially in weakly-hierarchical systems. The statistics support theidea that most multiple stars originated from dynamical interactions insmall clusters.
| The Visual Orbits of the Spectroscopic Binaries HD 6118 and HD 27483 from the Palomar Testbed Interferometer
We present optical interferometric observations of two double-linedspectroscopic binaries, HD 6118 and HD 27483, taken with the PalomarTestbed Interferometer (PTI) in the K band. HD 6118 is one of the mosteccentric spectroscopic binaries, and HD 27483 is a spectroscopic binaryin the Hyades open cluster. The data collected with PTI in 2001-2002allow us to determine astrometric orbits, which, when combined with theradial velocity measurements, determine all orbital parameters of thesystems. The masses of the components are 2.65+/-0.27 and2.36+/-0.24Msolar for HD 6118 and 1.38+/-0.13 and1.39+/-0.13Msolar for HD 27483. The apparent semimajor axisof HD 27483 is only 1.2 mas, making it the closest binary successfullyobserved with an optical interferometer.
| Near-Ultraviolet Spectra of Nine M Dwarf Stars, or a Second Effort to Find Optical Coronal Lines in M Dwarf Stars
We have searched for optical coronal lines in the 3100-3700 Åregion of eight M dwarf stars with rather low levels of activity. Thisbrief survey supplements a similar search in 15 active stars publishedin 1991. No coronal lines could be identified. However, the emissionspectra including lines of H I, He I, Ca II, Ca I, Si I, and Fe I aredescribed and illustrated. Radial velocities of the emission lines showno systematic differences from the stellar absorption lines. Coronaewith temperatures similar to those in the solar corona seem to be rareamong the M dwarfs, although at least one example has been found bySchmitt & Wichmann.
| 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.
| Stellar Coronal Astronomy
Coronal astronomy is by now a fairly mature discipline, with a quartercentury having gone by since the detection of the first stellar X-raycoronal source (Capella), and having benefitted from a series of majororbiting observing facilities. Serveral observational characteristics ofcoronal X-ray and EUV emission have been solidly established throughextensive observations, and are by now common, almost text-book,knowledge. At the same time the implications of coronal astronomy forbroader astrophysical questions (e.g.Galactic structure, stellarformation, stellar structure, etc.) have become appreciated. Theinterpretation of stellar coronal properties is however still often opento debate, and will need qualitatively new observational data to bookfurther progress. In the present review we try to recapitulate our viewon the status of the field at the beginning of a new era, in which thehigh sensitivity and the high spectral resolution provided by Chandraand SMM-Newton will address new questions which were not accessiblebefore.
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I.
We have embarked on a project, under the aegis of the Nearby Stars(NStars)/Space Interferometry Mission Preparatory Science Program, toobtain spectra, spectral types, and, where feasible, basic physicalparameters for the 3600 dwarf and giant stars earlier than M0 within 40pc of the Sun. In this paper, we report on the results of this projectfor the first 664 stars in the northern hemisphere. These resultsinclude precise, homogeneous spectral types, basic physical parameters(including the effective temperature, surface gravity, and overallmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. Observed and derived data presented in this paper arealso available on the project's Web site.
| Brightness Variations of SAO 84309
SAO 84309 varies in brightness with an amplitude of 0.1 magnitude and aperiod of 19 days.
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Draco |
| Ascensió Recta: | 18h33m55.77s |
| Declinació: | +51°43'08.9" |
| Magnitud Aparent: | 8.187 |
| Distancia: | 16.42 parsecs |
| Moviment propi RA: | 186 |
| Moviment propi Dec: | -325.9 |
| B-T magnitude: | 9.708 |
| V-T magnitude: | 8.313 |
Catàlegs i designacions:
|
