Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
Hunting the Coolest Dwarfs: Methods and Early Results
We present the methods and first results of a survey of nearby highproper motion main-sequence stars to probe for cool companions with theGemini camera at Lick Observatory. This survey uses a sample of old (age> 2 Gyr) stars as targets to probe for companions down totemperatures of 500 K. Multi-epoch observations allow us to discriminatecomoving companions from background objects. So far, our survey hassuccessfully rediscovered the wide T8.5 companion to GJ 1263 and hasdiscovered a companion to the nearby M0V star GJ 660.1. The companion toGJ 660.1 (GJ 660.1B) is ~4 mag fainter than its host star in the J-bandand is located at a projected separation of ~120 AU. Known trigonometricparallax and Two Micron All Sky Survey magnitudes for the GJ 660.1system indicate a spectral type for the companion of M9 ± 2.
| Near-infrared K and L' Flux Ratios in Six Lensed Quasars
We examine the wavelength dependence of flux ratios for sixgravitationally lensed quasars using K and L' images obtained at theGemini North 8 m telescope. We select lenses with source redshiftszs < 2.8 so that K-band images probe rest-frame opticalemission from accretion disks, while L'-band images probe rest-framenear-infrared flux emitted (in part) from the more extended surroundingtorus. Since the observations correspond to different source sizes, theK and L' flux ratios are sensitive to structure on different scales andmay be useful for studying small structure in the lens galaxies. Four ofthe six lenses show differences between K and L' flux ratios. In HE0435-1223, SDSS 0246-0825, and HE 2149-2745, the differences may beattributable to known microlensing and/or intrinsic variability. In SDSS0806+2006, the wavelength dependence is not easily attributed to knownvariations and may indicate the presence of substructure. By contrast,in Q0142-100 and SBS 0909+523 the K and L' flux ratios are consistentwithin the uncertainties. We discuss the utility of the current data forstudying chromatic effects related to microlensing, dust extinction, anddark matter substructure.
| UBV(RI)C JHK observations of Hipparcos-selected nearby stars
We present homogeneous, standardized UBV(RI)C photometry forover 700 nearby stars selected on the basis of Hipparcos parallaxes.Additionally, we list JHK photometry for about half of these stars, aswell as L photometry for 86 of the brightest. A number of stars withpeculiar colours or anomalous locations in various colour-magnitudediagrams are discussed.
| The AU Microscopii Debris Disk: Multiwavelength Imaging and Modeling
Debris disks around main-sequence stars are produced by the destructionof unseen parent bodies. AU Microscopii (GJ 803) is a compelling objectto study in the context of disk evolution across different spectraltypes, as it is an M dwarf whose nearly edge-on disk may be directlycompared to that of its A5 V sibling ? Pic. We resolve the diskfrom 8-60 AU in the near-IR JHK' bands at high resolution with the KeckII Telescope and adaptive optics, and develop a data reduction techniquefor the removal of the stellar point-spread function. We measure a bluecolor across the near-IR bands, and confirm the presence of substructurein the inner disk. Some of the structural features exhibitwavelength-dependent positions. Recent measurements of thescattered-light polarization indicate the presence of porous grains. Thescattering properties of these porous grains have a strong effect on theinferred structure of the disk relative to the majority of previouslymodeled grain types. Complementing prior work, we use a Monte Carloradiative transfer code to compare a relatively simple model of thedistribution of porous grains to a broad data set, simultaneouslyfitting midplane surface brightness profiles and the spectral energydistribution. Our model confirms that the large-scale architecture ofthe disk is consistent with detailed models of steady state graindynamics. A belt of parent bodies from 35-40 AU produces dust that isthen swept outward by stellar wind and radiation. We infer the presenceof very small grains in the region exterior to the belt, down to sizesof ~0.05 ?m. These sizes are consistent with stellar mass-loss ratesM?*<<102 M?solar
| Optical spectroscopy of high proper motion stars: new M dwarfs within 10 pc and the closest pair of subdwarfs
We present spectra of 59 nearby star candidates, M dwarfs and whitedwarfs, previously identified using high proper motion catalogues andthe DENIS database. We review the existing spectral classificationschemes and spectroscopic parallax calibrations in the near-infrared Jband and derive spectral types and distances of the nearby candidates.Forty-two stars have spectroscopic distances smaller than 25 pc, threeof them being white dwarfs. Two targets lie within 10 pc, one M8 star at10.0 pc (APMPM J0103-3738), and one M4 star at 8.3 pc (L 225-57). Onestar, LHS 73, is found to be among the few subdwarfs lying within 20 pc.Furthermore, together with LHS 72, it probably belongs to the closestpair of subdwarfs we know.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| L' and M' Photometry of Ultracool Dwarfs
We have compiled L' (3.4-4.1 μm) and M' (4.6-4.8 μm) photometry of63 single and binary M, L, and T dwarfs obtained at the United KingdomInfrared Telescope using the Mauna Kea Observatory filter set. Thiscompilation includes new L' measurements of eight L dwarfs and 13 Tdwarfs and new M' measurements of seven L dwarfs, five T dwarfs, and theM1 dwarf Gl 229A. These new data increase by factors of 0.6 and 1.6,respectively, the numbers of ultracool dwarfs (Teff<~2400K) for which L' and M' measurements have been reported. We computeLbol, BCK, and Teff for 42 dwarfs whoseflux-calibrated JHK spectra, L' photometry, and trigonometric parallaxesare available, and we estimate these quantities for nine other dwarfswhose parallaxes and flux-calibrated spectra have been obtained.BCK is a well-behaved function of near-infrared spectral typewith a dispersion of ~0.1 mag for types M6-T5 it is significantly morescattered for types T5-T9. Teff declines steeply andmonotonically for types M6-L7 and T4-T9, but it is nearly constant at~1450 K for types L7-T4 with assumed ages of ~3 Gyr. This constantTeff is evidenced by nearly unchanging values of L'-M'between types L6 and T3. It also supports recent models that attributethe changing near-infrared luminosities and spectral features across theL-T transition to the rapid migration, disruption, and/or thinning ofcondensate clouds over a narrow range of Teff. The L' and M'luminosities of early-T dwarfs do not exhibit the pronounced humps orinflections previously noted in the I through K bands, but insufficientdata exist for types L6-T5 to assert that ML' andMM' are strictly monotonic within this range of types. Wecompare the observed K, L', and M' luminosities of L and T dwarfs in oursample with those predicted by precipitating-cloud and cloud-free modelsfor varying surface gravities and sedimentation efficiencies. The modelsindicate that the L3-T4.5 dwarfs generally have higher gravities(logg=5.0-5.5) than the T6-T9 dwarfs (logg=4.5-5.0). The predicted M'luminosities of late-T dwarfs are 1.5-2.5 times larger than thosederived empirically for the late-T dwarfs in our sample. Thisdiscrepancy is attributed to absorption at 4.5-4.9 μm by CO, which isnot expected under the condition of thermochemical equilibrium assumedin the models. Our photometry and bolometric calculations indicate thatthe L3 dwarf Kelu-1 and the T0 dwarf SDSS J042348.57-041403.5 areprobable binary systems. We computelog(Lbol/Lsolar)=-5.73+/-0.05 andTeff=600-750 K for the T9 dwarf 2MASSI J0415195-093506, whichsupplants Gl 570D as the least luminous and coolest brown dwarfpresently known.
| L' and M' standard stars for the Mauna Kea Observatories Near-Infrared system
We present L' and M' photometry, obtained at the United Kingdom InfraredTelescope (UKIRT) using the Mauna Kea Observatories Near-Infrared(MKO-NIR) filter set, for 46 and 31 standard stars, respectively. The L'standards include 25 from the in-house `UKIRT Bright Standards' withmagnitudes deriving from Elias et al. and observations at the InfraredTelescope Facility in the early 1980s, and 21 fainter stars. The M'magnitudes derive from the results of Sinton and Tittemore. We estimatethe average external error to be 0.015 mag for the bright L' standardsand 0.025 mag for the fainter L' standards, and 0.026 mag for the M'standards. The new results provide a network of homogeneously observedstandards, and establish reference stars for the MKO system, in thesebands. They also extend the available standards to magnitudes whichshould be faint enough to be accessible for observations with moderndetectors on large and very large telescopes.
| JHK Standard Stars on the CIT Photometric System
We present a set of 58 stars with JHK standard values on the CIT systemand with a suitable magnitude range for use with array detectors onsmall- to moderate-size telescopes. Each final value is based on six to47 measures (with a mean of 17) obtained on separate nights with the USNaval Observatory (USNO) NICMOS3 (HgCdTe) camera. The objects include 20primary CIT standards from Elias et al. and 38 secondary sourcesselected from the SAAO and UKIRT standards lists, cover a K-magnituderange between 6.0 and 10.8, and lie north of declination -20°. Thestars were reduced to the CIT system as defined by Elias et al.,producing a USNO system that is identical to the near-infrared CITsystem. This work densifies the original CIT system by nearly a factorof 3 and extends its range by about 3 mag. The SAAO and UKIRT standardsare also compared with the CIT system.
| Near-Infrared Photometric Survey of Proto-planetary Nebula Candidates
We present JHK' photometric measurements of 78 objects mostly consistingof proto-planetary nebula candidates. Photometric magnitudes aredetermined by means of imaging and aperture photometry. Unlike theobservations with a photometer with a fixed-sized beam, the method ofimaging photometry permits accurate derivation of photometric values,because the target sources can be correctly identified and confusionwith neighboring sources can be easily avoided. Of the 78 sourcesobserved, we report nearly 10 cases in which the source seems to havebeen misidentified or confused by nearby bright sources. We also presentnearly two dozen cases in which the source seems to have indicated avariability that prompts a follow-up monitoring. There are also a fewsources that show previously unreported extendedness. In addition, wepresent H-band finding charts of the target sources.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| H II Emission from a Complete Spectroscopic Survey of Be Stars in h and χ Persei
We describe data for emission-line B stars observed in a spectroscopicsurvey of h and χ Persei. The survey is complete to V=12.5 andcovers an area of ~1100 arcmin2 roughly centered on the twoclusters. We detect 32 Be stars; some have low Hα emissionstrength. Seven of these are new identifications; seven others areconfirmations of Be stars previously identified using photometry. Fiveof the observed Be stars show significant Hα profile variationsfrom epoch to epoch. We show that spectral indices yield physicalcharacteristics of the H II emission region. This automatic method isrobust and easily applied to large spectroscopic samples. We inferHα:Hβ flux ratios of 2-5 and observe a linear relationshipbetween Hα emission and J-K color for these stars. We include aHertzsprung-Russell diagram for the B-type stars in the clusters.
| Revised Coordinates and Proper Motions of the Stars in the Luyten Half-Second Catalog
We present refined coordinates and proper-motion data for the highproper-motion (HPM) stars in the Luyten Half-Second (LHS) catalog. Thepositional uncertainty in the original Luyten catalog is typicallygreater than 10" and is often greater than 30". We have used the digitalscans of the POSS I and POSS II plates to derive more accurate positionsand proper motions of the objects. Out of the 4470 candidates in the LHScatalog, 4323 objects were manually reidentified in the POSS I and POSSII scans. A small fraction of the stars were not found because of thelack of finder charts and digitized POSS II scans. The uncertainties inthe revised positions are typically ~2" but can be as high as ~8" in afew cases, which is a large improvement over the original data.Cross-correlation with the Tycho-2 and Hipparcos catalogs yielded 819candidates (with mR<~12). For these brighter sources, theposition and proper-motion data were replaced with the more accurateTycho-2/Hipparcos data. In total, we have revised proper-motionmeasurements and coordinates for 4040 stars and revised coordinates for4330 stars. The electronic version of the paper5 contains the updated information on all 4470stars in the LHS catalog.
| The Palomar/MSU Nearby Star Spectroscopic Survey. III. Chromospheric Activity, M Dwarf Ages, and the Local Star Formation History
We present high-resolution echelle spectroscopy of 676 nearby M dwarfs.Our measurements include radial velocities, equivalent widths ofimportant chromospheric emission lines, and rotational velocities forrapidly rotating stars. We identify several distinct groups by theirHα properties and investigate variations in chromospheric activityamong early (M0-M2.5) and mid (M3-M6) dwarfs. Using a volume-limitedsample together with a relationship between age and chromosphericactivity, we show that the rate of star formation in the immediate solarneighborhood has been relatively constant over the last 4 Gyr. Inparticular, our results are inconsistent with recent large bursts ofstar formation. We use the correlation between Hα activity and ageas a function of color to set constraints on the properties of L and Tdwarf secondary components in binary systems. We also identify a numberof interesting stars, including rapid rotators, radial velocityvariables, and spectroscopic binaries. Observations were made at the 60inch telescope at Palomar Mountain, which is jointly owned by theCalifornia Institute of Technology and the Carnegie Institution ofWashington.
| Meeting the Cool Neighbors. I. Nearby Stars in the NLTT Catalogue: Defining the Sample
We are currently undertaking a program aimed at identifying previouslyunrecognized late-type dwarfs within 20 pc of the Sun. As a first step,we have cross-referenced Luyten's NLTT proper-motion catalog against thesecond incremental release of the Two Micron All Sky Survey (2MASS)Point Source Catalog and use optical/infrared colors, derived bycombining Luyten's mr estimates with 2MASS data, to identifycandidate nearby stars. This paper describes the definition of areference sample of 1245 stars and presents a compilation of literaturedata for more than one-third of the sample. Only 274 stars havetrigonometric parallax measurements, but we have used data for nearbystars with well-determined trigonometric parallaxes to computecolor-magnitude relations in the (MV, V-K), (MV,V-I), and (MI, I-J) planes and use those relations todetermine photometric parallaxes for NLTT stars with optical photometry.Based on the 2MASS JHKs data alone, we have identified afurther 42 ultracool dwarfs (J-Ks>0.99) and useJ-Ks colors to estimate photometric parallaxes. Combiningthese various techniques, we identify 308 stars with formal distances ofless than 20 pc, while a further 46 have distance estimates within 1σ of our survey limit. Of these 354 stars, 75, including 39 of theultracool dwarfs, are new to nearby-star catalogs. Two stars with bothoptical and near-infrared photometry are potential additions to theimmediate solar neighborhood, with formal distance estimates of lessthan 10 pc.
| Toward Spectral Classification of L and T Dwarfs: Infrared and Optical Spectroscopy and Analysis
We present 0.6-2.5 μm, R>~400 spectra of 27 cool, low-luminositystars and substellar objects. Based on these and previously publishedspectra, we develop a preliminary spectral classification system for Land T dwarfs. For late L and T types the classification system is basedentirely on four spectral indices in the 1-2.5 μm interval. Two ofthese indices are derived from water absorption bands at 1.15 and 1.4μm, the latter of which shows a smooth increase in depth through theL and T sequences and can be used to classify both spectral types. Theother two indices make use of methane absorption features in the H and Kbands, with the K-band index also applicable to mid-to-late L dwarfs.Continuum indices shortward of 1 μm used by previous authors toclassify L dwarfs are found to be useful only through mid-L subclasses.We employ the 1.5 μm water index and the 2.2 μm methane index tocomplete the L classification through L9.5 and to link the new systemwith a modified version of the 2MASS ``color-d'' index. By correlatingthe depths of the methane and water absorption features, we establish aT spectral sequence from T0 to T8, based on all four indices, that is asmooth continuation of the L sequence. We reclassify two 2MASS L8 dwarfsas L9 and L9.5 and identify one SDSS object as L9. In the proposedsystem methane absorption appears in the K band approximately at L8, twosubclasses earlier than its appearance in the H band. The L and Tspectral classes are distinguished by the absence and presence,respectively, of H-band methane absorption.
| 5 Micron Photometry of Late-Type Dwarfs
We present narrowband M photometry of nine low-mass dwarfs with spectraltypes ranging from M2.5 to L0.5. Combining the (L'-M') colors derivedfrom our observations with data from the literature, we find colorsconsistent with a Rayleigh-Jeans flux distribution for spectral typesearlier than M5, but enhanced F3.8/F4.7 fluxratios (negative [L'-M'] colors) at later spectral types. This probablyreflects increased absorption at M' due to the CO fundamental band. Wecompare our results against recent model predictions and briefly discussthe implications.
| Are Magnetically Active Low-Mass M Dwarfs Completely Convective?
Stars on the main sequence are expected to be completely convective iftheir mass lies below a certain value, Mcc. Standard stellarstructure codes suggest that Mcc is in the range 0.3-0.4Msolar. In the present paper we examine several nonstandardadditions to stellar structure in order to quantify their effects on thevalue of Mcc. We find that by including magnetic fieldeffects, Mcc may fall to values that are significantlysmaller than the standard range. This result is of interest inunderstanding why coronae and chromospheres in active M dwarfs fail toexhibit detectable alterations at spectral class M3-M4. The structuralproperties of our magnetic models also explain why active M dwarfs tendto have radii that are larger than expected for their Teffvalues or Teff values that are too low for their radii. Ourresults lead us to predict that certain stars that are classified aslate L or T stars may actually have masses of 0.1-0.15Msolar.
| Spectral Energy Distributions for Disk and Halo M Dwarfs
We have obtained infrared (1-2.5 ?m) spectroscopy for 42 halo anddisk dwarfs with spectral types M1-M6.5. These data are compared tosynthetic spectra generated by the latest model atmospheres of Allard& Hauschildt. Photospheric parameters metallicity, effectivetemperature, and radius are determined for the sample.We find goodagreement between observation and theory except for known problems dueto incomplete molecular data for metal hydrides and H2O. Themetal-poor M subdwarfs are well matched by the models, as oxide opacitysources are less important in this case. The derived effectivetemperatures for the sample range from 3600 to 2600 K; at thesetemperatures grain formation and extinction are not significant in thephotosphere. The derived metallicities range from solar to 1/10 solar.The radii and effective temperatures derived agree well with recentmodels of low-mass stars. The spectra are available in electronic formupon request.
| BY Draconis is a Triple Star System.
We have discovered that the nearby double-lined spectroscopic binary BYDraconis has a proper motion companion 17 arcsec to the northeast.Photometric measurements indicate that the companion is an M5 dwarflying on the main sequence. Studies of this third component could provevaluable in determining the evolutionary state of the system.
| Multiwavelength Observations of Collisional Ring Galaxies.I.Broad-Band Images, Global Properties, and Radial Colors of the Sample Galaxies
This is one of a series of papers discussing the optical, infrared andradio continuum properties of a sample of collisional ring galaxies. Thepresent paper concentrates on the global broad-band optical (B, V and R)and near-IR (J, H and K) images of the galaxies and describe theirglobal properties. An analysis of the colors of the galaxies over avariety of wavelength baselines is described. In the B and V bands, thebluest colors are found in the outer bright ring. The B-V colors of thesample of galaxies are blue, the median value for the sample is B-V =0.60, and V-K= 2.33 mag. The IR morphology of the galaxies is, in mostcases, very similar to that of the B-band data, suggesting that theclumpy appearance of the star formation in the outer rings is real, andnot a result of patchy dust obscuration. Only in one ring (WN1, aSeyfert ring galaxy) was the IR morphology different from the optical,suggesting the presence of significant dust in the disk. In II Hz 4,faint spiral arms are seen within the ring. There is a suggestion thatthe larger rings have redder V-K colors, which may be due to anincreased incidence of nuclear bulges in larger ring galaxies. Radialprofiles of surface brightness and color are presented for fourgalaxies. In all cases, the colors becomes bluer as one proceedsradially outwards, but in two galaxies, the rings redden again outsidethe main ring, suggesting the existence of a red stellar population thatmay have pre-dated the collisions.
| The Palomar/MSU Nearby Star Spectroscopic Survey.II.The Southern M Dwarfs and Investigation of Magnetic Activity
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2799H&db_key=AST
| The unusual circumstellar environment of the evolved star, U Equulei.
In the course of a spectroscopic survey to identify cold IRAS stars, wediscovered that the evolved star, U Equ, has a very peculiar opticalspectrum indicating an unusual circumstellar environment. The moderateresolution (62A/mm) spectrum has deep, yet unusually thin, molecularabsorption features that must arise in cold gas at a large distance fromthe star. The optical spectrum also has striking molecular emissionlines of TiO, AlO, VO possibly due to a fluorescence mechanism. Althoughthe IRAS 25/12μm colors of U Equ are typical of optically thincircumstellar envelopes, the LRS spectrum displays a strong 10 μmsilicate absorption band, indicating a thick, dusty envelope. Comparingour H_2_O and OH maser observations with profiles in the literaturetaken in 1987 (H_2_O) and 1990 (OH), we have found a variable velocitypattern and profile shape. We suggest that the star is of a warmspectral type, G to early K, and that it has an edge-on dusty disk ortorus and an inner warm molecular circumstellar shell. The luminositycriteria in our moderate-resolution spectra are consistent with that ofan evolved giant. The velocity and Galactic latitude are not consistentwith an early pre-main sequence evolutionary stage; however, theline-of-sight proximity of U Equ and a bright ribbon of IRAS Galacticcirrus suggest further investigation into the interstellar environmentis needed. We present optical spectra, profiles of the H_2_O and OHmasers, and J and K band images and photometry.
| 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.
| The Palomar/MSU Nearby-Star Spectroscopic Survey. I. The Northern M Dwarfs -Bandstrengths and Kinematics
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.1838R&db_key=AST
| Multiwavelength observations of ring galaxies. 2: Global star formation in ring galaxies
We present optical H-alpha emission-line images and K band near-infraredimages of a sample of collisionally formed ring galaxies. These are usedto determine the distribution of star formation and the distribution ofthe old stellar population, respectively, in the galaxies. Our resultsshow ring galaxies to have similar Hcx luminosities to starburstgalaxies, with star formation being contained almost exclusively in thering. In the larger ring galaxies we observe the ionized hydrogen to lieon the outer edge of the underlying, broader, K band ring. No conclusiveevidence is found in our sample for a true underlying stellar densitywave. Rather, the evidence suggests that either the density waves havepassed into the outer, mainly H I disk of the galaxies or that theprogenitor galaxies were mainly gas-rich low surface brightness objectsand that most of the optical/IR light we now observe has resulted fromrecent star formation in the expanding ring.
| The general catalogue of trigonometric [stellar] paralaxes
Not Available
| The faintest stars - Infrared photometry, spectra, and bolometric magnitude
Infrared JHKLL-prime photometry, and low resolution IF spectra arepresented for the faintest stars. The stellar H2O bands which dominatethe atmospheres of these stars were studied. L band fluxes of thesestars are considerably depressed relative to L prime fluxes by thepresence of stellar H2O absorption. Strong H2O absorption is observed inthese infrared spectra. The amount of flux which is 'overcounted' whenH2O absorption bands are ignored is examined. Bolometric fluxes arecalculated using broadband photometry alone, requiring a correction ofonly approximately 5 percent to 10 percent. Photometric and spectraldata is used to evaluate bolometric corrections and magnitudes of asample of late type M dwarfs.
| Infrared colors of low-mass stars
A total of 322 red dwarf stars are studied in a review of IR IJHKphotometry to discern chromospheric activity and kinematic dataregarding metallicity effects in the IR color:color diagrams. Themetallicity variations are employed to assess changes in the H(-)continuum opacity and water-vapor characterizations. The stars areclassified in terms of metal-richness with five categories includingyoung disk, old disk, and halo types with attention given to the inverserelationship between metallicity and water-band absorption strength. Theresults include IR photometric parallax relations for each metallicitygroup and absolute magnitudes for single stars as well as temperatures,intrinsic colors, and spectral types. The body of data is useful forconstraining models of the interiors and atmospheres of this class ofstars.
| A filter for deep near-infrared imaging
The K passband (central wavelength 2.2 microns, FWHM 0.4 micron) is thelongest wavelength standard near-IR passband through which deepground-based imaging is possible. Thermal emission from telescope,instrument, and sky limits the depth to which such imaging can reach byproducing strongly temperature-dependent backgrounds in the range11-13.5 mag/sq arcsec. This paper describes how a passband, which isdenoted as K-prime, located slightly shortward of the standard Kpassband (central wavelength 2.1 microns), yet still within the sameatmospheric window, leads to a significantly lower thermal component ofthe background, reducing the background surface brightness by up to 0.9mag sq arcsec, and thereby allowing deeper imaging to be obtained in thesame integration time. The photometric differences between the K-primefilter and the standard K filter are discussed.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Kova |
| Sað Açýklýk: | 20h56m46.60s |
| Yükselim: | -10°26'54.9" |
| Görünürdeki Parlaklýk: | 11.465 |
| Uzaklýk: | 14.769 parsek |
| özdevim Sað Açýklýk: | -41.5 |
| özdevim Yükselim: | -1130.6 |
| B-T magnitude: | 13.858 |
| V-T magnitude: | 11.663 |
Kataloglar ve belirtme:
|
