תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
Doppler splitting in diffuse interstellar bands
We demonstrate evident Doppler splitting in the profiles of many narrowdiffuse interstellar bands (DIBs). Their components are compared withthose of atomic and molecular lines of interstellar origin. It is shownthat it is likely that the species that shares both wavelength shiftsand strength ratios of the Doppler components seen in the DIB profilesis the CH radical. Because of this profile resemblance, it isrecommended that CH lines can be used to shift spectra to the restvelocity frame for interstellar features, especially to determine theDIB rest wavelengths on the basis of the CH line at 4300.3132 Å inthe spectrum of HD147889. Our results strongly support a molecularorigin of diffuse bands.
| A systematic study of variability among OB-stars based on HIPPARCOS photometry
Context: Variability is a key factor for understanding the nature of themost massive stars, the OB stars. Such stars lie closest to the unstableupper limit of star formation. Aims: In terms of statistics, thedata from the HIPPARCOS satellite are unique because of time coverageand uniformity. They are ideal to study variability in this large,uniform sample of OB stars. Methods: We used statisticaltechniques to determine an independant threshold of variabilitycorresponding to our sample of OB stars, and then applied an automaticalgorithm to search for periods in the data of stars that are locatedabove this threshold. We separated the sample stars into 4 maincategories of variability: 3 intrinsic and 1 extrinsic. The intrinsiccategories are: OB main sequence stars (~2/3 of the sample), OBe stars(~10%) and OB Supergiant stars (~1/4).The extrinsic category refers toeclipsing binaries. Results: We classified about 30% of the wholesample as variable, although the fraction depends on magnitude level dueto instrumental limitations. OBe stars tend to be much more variable(≈80%) than the average sample star, while OBMS stars are belowaverage and OBSG stars are average. Types of variables include αCyg, β Cep, slowly pulsating stars and other types from the generalcatalog of variable stars. As for eclipsing binaries, there arerelatively more contact than detached systems among the OBMS and OBestars, and about equal numbers among OBSG stars.
| CaII K interstellar observations towards early-type disc and halo stars, abundances and distances of intermediate- and high-velocity clouds
We present CaII K (λair = 3933.661Å)interstellar observations towards 20 early-type stars, to place lowerdistance limits to intermediate- and high-velocity clouds (IHVCs) intheir lines of sight. The spectra are also employed to estimate the Caabundance in the low-velocity gas towards these objects, when combinedwith Leiden-Dwingeloo 21-cm HI survey data of spatial resolution . Nineof the stars, which lie towards IHVC complexes H, K and gp, wereobserved with the intermediate dispersion spectrograph on the IsaacNewton Telescope at a resolution R = λ/Δλ of 9000(~33kms-1) and signal-to-noise ratio (S/N) per pixel of75-140. A further nine objects were observed with the Utrecht EchelleSpectrograph on the William Herschel Telescope at R = 40000(~7.5kms-1) and S/N per pixel of 10-25. Finally, two objectswere observed in both CaII K and NaI D lines using the 2D COUDÉspectrograph on the McDonald 2.7-m telescope at R = 35000 (~8.5kms-1). The abundance of CaII K {log10(A) =log10[N(CaII K)]-log10[N(HI)]} plotted against HIcolumn density for the objects in the current sample with heights abovethe Galactic plane (z) exceeding 1000pc is found to obey the Wakker& Mathis (2000) relation. Also, the reduced column density of CaII Kas function of z is consistent with the larger sample taken from Smokeret al. (2003). Higher S/N observations than those previously takentowards HVC complex H stars HD13256 and HILT 190 reinforce the assertionthat this lies at a distance exceeding 4000pc. No obvious absorption isdetected in observations of ALS10407 and HD357657 towards IVC complexgp. The latter star has a spectroscopically estimated distance of~2040pc, although this was derived assuming the star lies on the mainsequence and without any reddening correction being applied. Finally, noCaII K absorption is detected towards two stars along the line of sightto complex K, namely PG1610+529 and PG1710+490. The latter is at adistance of ~700pc, hence placing a lower distance limit to thiscomplex, where previously only an upper distance limit of 6800pc wasavailable.
| On the diffuse bands related to the C2 interstellar molecule
The recently published idea that intensities of some weak diffuseinterstellar bands (DIBs) are related to the C2 molecule column densityhave been examined. We use a set of high quality echelle spectra ofheavily reddened stars, acquired at the Bohyunsan Optical AstronomicalObservatory (South Korea), with a resolution R=30 000. The high quality(high S/N ratio) of our spectra is proved by the fact that despite usingthe most widely used Phillips (2, 0) band of the C2 molecule (near 8760Å), we can trace the (3, 0) Phillips band (near 7725 Å) aswell. Equivalent widths of four (5176, 5542, 5546 and 5769 Å) outof 16 examined DIBs demonstrate relatively good correlation with C2column density. However, a majority of the studied DIBs, alreadyreported as "C2" ones, most likely are not related to this simplestcarbon molecule. A removal of peculiar objects like HD 34078 from theanalyzed sample does not substantially change the level of correlations.
| Interstellar Ca II Line Intensities and the Distances of the OB stars
We show that the equivalent widths of the well-known interstellar Ca IIH and K lines can be used to determine the distances to OB stars in ourGalaxy. The equivalent widths, measured in the spectra of 147 early-typestars, are strongly related to the Hipparcos parallaxes of thoseobjects. The lines fitted to the parallax-equivalent width data aregiven by the formulae π=1/[2.78EW(K)+95] and π=1/[4.58EW(H)+102],where π is in arcseconds and EW is in milliangstroms. The form of theformulae, yielding a finite parallax even for zero absorption, showsthat space within ~100 pc of the Sun contains very little Ca II, whichis in agreement with the known dimensions of the Local Bubble. Using CaII lines for distance determination does not require the knowledge ofthe absolute magnitude of the object; it is thus well suited for targetsfor which the absolute calibration is either not precise (OBsupergiants) or not available at all (peculiar objects). We alsodemonstrate that neither the reddening E(B-V) nor the equivalent widthsof interstellar K I and CH lines are suitable candidates for distanceestimation, their relation with parallaxes being far less tight than forCa II.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Observations of Star-Forming Regions with the Midcourse Space Experiment
We have imaged seven nearby star-forming regions, the Rosette Nebula,the Orion Nebula, W3, the Pleiades, G300.2-16.8, S263, and G159.6-18.5,with the Spatial Infrared Imaging Telescope on the Midcourse SpaceExperiment (MSX) satellite at 18" resolution at 8.3, 12.1, 14.7, and21.3 μm. The large angular scale of the regions imaged (~7.2-50deg2) makes these data unique in terms of the combination ofsize and resolution. In addition to the star-forming regions, twocirrus-free fields (MSXBG 160 and MSXBG 161) and a field near the southGalactic pole (MSXBG 239) were also imaged. Point sources have beenextracted from each region, resulting in the identification over 500 newsources (i.e., no identified counterparts at other wavelengths), as wellas over 1300 with prior identifications. The extended emission from thestar-forming regions is described, and prominent structures areidentified, particularly in W3 and Orion. The Rosette Nebula isdiscussed in detail. The bulk of the mid-infrared emission is consistentwith that of photon-dominated regions, including the elephant trunkcomplex. The central clump, however, and a line of site toward thenorthern edge of the cavity show significantly redder colors than therest of the Rosette complex.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| The association of IRAS sources and 12CO emission in the outer Galaxy
We have revisited the question of the association of CO emission withIRAS sources in the outer Galaxy using data from the FCRAO Outer GalaxySurvey (OGS). The availability of a large-scale high-resolution COsurvey allows us to approach the question of IRAS-CO associations from anew direction - namely we examined all of the IRAS sources within theOGS region for associated molecular material. By investigating theassociation of molecular material with random lines of sight in the OGSregion we were able to construct a quantitative means to judge thelikelihood that any given IRAS-CO association is valid and todisentangle multiple emission components along the line of sight. Thepaper presents a list of all of the IRAS-CO associations in the OGSregion. We show that, within the OGS region, there is a significantincrease ( ~ 22%) in the number of probable star forming regions overprevious targeted CO surveys towards IRAS sources. As a demonstration ofthe utility of the IRAS-CO association table we present the results ofthree brief studies on candidate zone-of-avoidance galaxies with IRAScounterparts, far outer Galaxy CO clouds, and very bright CO clouds withno associated IRAS sources. We find that ~ 25% of such candidate ZOAGsare Galactic objects. We have discovered two new far outer Galaxystar-forming regions, and have discovered six bright molecular cloudsthat we believe are ideal targets for the investigation of the earlieststages of sequential star formation around HII regions. Finally, thispaper provides readers with the necessary data to compare othercatalogued data sets with the OGS data.Tables 1, 2 and A1 are 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/399/1083
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| GSH 138-01-94: An Old Supernova Remnant in the Far Outer Galaxy
The properties of the Galactic H I shell GSH 138-01-94 are derived fromdata of the Canadian Galactic Plane Survey. The basic parameters of GSH138-01-94 were determined by fitting the expansion of a thin shell tothe expansion velocity field on the sky. The kinematic distance is 16.6kpc for vLSR=-94.2+/-0.5kms-1. The radius is180+/-10pc, the expansion velocityvexp=11.8+/-0.9kms-1, and the mass2×105Msolar. No radio-continuum counterpartof the shell was detected at 21 cm or at 74 cm. Absorption of abackground continuum source constrains the spin temperature of H I inthe shell to Ts=230367173K. Theexpansion age of GSH 138-01-94 is 4.3 Myr. These observables are inexcellent agreement with predictions from hydrodynamic models for asupernova remnant in a low-density, low-metallicity environment such asthe outer Galaxy. GSH 138-01-94 is then the largest and the oldestsupernova remnant known. It provides direct evidence for the release ofmechanical energy in the interstellar medium by stars in the outerGalaxy. We argue that such old supernova remnants are to be found inlow-density, low-metallicity environments such as the outer Galaxy,dwarf galaxies, and low surface brightness galaxies.
| Distances and Metallicities of High- and Intermediate-Velocity Clouds
A table is presented that summarizes published absorption linemeasurements for the high- and intermediate-velocity clouds (HVCs andIVCs). New values are derived for N(H I) in the direction of observedprobes, in order to arrive at reliable abundances and abundance limits(the H I data are described in Paper II). Distances to stellar probesare revisited and calculated consistently, in order to derive distancebrackets or limits for many of the clouds, taking care to properlyinterpret nondetections. The main conclusions are the following. (1)Absolute abundances have been measured using lines of S II, N I, and OI, with the following resulting values: ~0.1 solar for one HVC (complexC), ~0.3 solar for the Magellanic Stream, ~0.5 solar for a southern IVC,and ~solar for two northern IVCs (the IV Arch and LLIV Arch). Finally,approximate values in the range 0.5-2 solar are found for three moreIVCs. (2) Depletion patterns in IVCs are like those in warm disk or halogas. (3) Most distance limits are based on strong UV lines of C II, SiII, and Mg II, a few on Ca II. Distance limits for major HVCs aregreater than 5 kpc, while distance brackets for several IVCs are in therange 0.5-2 kpc. (4) Mass limits for major IVCs are0.5-8×105 Msolar, but for major HVCs theyare more than 106 Msolar. (5) The Ca II/H I ratiovaries by up to a factor 2-5 within a single cloud, somewhat morebetween clouds. (6) The Na I/H I ratio varies by a factor of more than10 within a cloud, and even more between clouds. Thus, Ca II can beuseful for determining both lower and upper distance limits, but Na Ionly yields upper limits.
| The H I Shell G132.6-0.7-25.3: A Supernova Remnant or an Old Windblown Bubble?
Data from the Canadian Galactic Plane Survey reveal an abundance of H Ishells and arcs in the disk of our galaxy. While their shape suggeststhe influence of stellar winds or supernovae, very few of thesestructures have been examined in detail thus far. A fine example is an HI shell in the outer Galaxy with no continuum counterpart, discovered inthe survey's pilot project. Its size and kinematics suggest that it wascreated by the winds of a single late-type O star that has since evolvedoff the main sequence, or by a supernova explosion. A B1 Ia star at thecenter of the shell, in projection, is a possible candidate for theenergy source if the shell is assumed to be windblown. The shell's shapeimplies a surprisingly small scale height of less than about 30 pc forthe surrounding gas if the elongation is due to evolution in a densitygradient.
| Detection of CO and Dust Emission in Near-Infrared Spectra of SN 1998S
Near-infrared spectra (0.95-2.4 ?m) of the peculiar Type IInsupernova 1998S in NGC 3877 from 95 to 355 days after maximum light arepresented. K-band data taken at days 95 and 225 show the presence of thefirst overtone of CO emission near 2.3 ?m, which is gone by day 355.An apparent extended blue wing on the CO profile in the day 95 spectrumcould indicate a large CO expansion velocity (~2000-3000 kms-1). This is the third detection of infrared CO emission innearly as many Type II supernovae studied, implying that moleculeformation may be fairly common in Type II events and that the earlyformation of molecules in SN 1987A may be typical rather thanexceptional. Multipeak hydrogen and helium lines suggest that SN 1998Sis interacting with a circumstellar disk, and the fading of the red sideof this profile with time suggests that dust is forming in the ejecta,perhaps induced by CO cooling. Continuum emission that rises towardlonger wavelengths (J-->K) is seen after day 225 with an estimatednear-infrared luminosity >~1040 ergs s-1. Thismay be related to the near-infrared excesses seen in a number of othersupernovae. If this continuum is due to free-free emission, it requiresan exceptionally shallow density profile. On the other hand, the shapeof the continuum is well fitted by a 1200+/-150 K blackbody spectrum,possibly due to thermal emission from dust. Interestingly, we observe asimilar 1200 K blackbody-like, near-infrared continuum in SN 1997ab,another Type IIn supernova at an even later postmaximum epoch (day1064+). A number of dust emission scenarios are discussed, and weconclude that the near-infrared dust continuum is likely powered by theinteraction of SN 1998S with the circumstellar medium.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Catalogue of H-alpha emission stars in the Northern Milky Way
The ``Catalogue of Stars in the Northern Milky Way Having H-alpha inEmission" appears in Abhandlungen aus der Hamburger Sternwarte, Band XIin the year 1997. It contains 4174 stars, range {32degr <= l() II< 214degr , -10degr < b() II < +10degr } having the Hαline in emission. HBH stars and stars of further 99 lists taken from theliterature till the end of 1994 were included in the catalogue. We givethe cross-identification of stars from all lists used. The catalogue isalso available in the Centre de Données, Strasbourg ftp130.79.128.5 or http://cdsweb.u-strasbg.fr and at the HamburgObservatory via internet.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| Equivalent width of NA I and K I lines and reddening.
The profile, radial velocity and equivalent width of the interstellarlines of Na I (5890.0, 5895.9Å) and K I (7699.0Å) have beenobtained from Echelle+CCD observations at resolving powerλ/{DELTA}λ~16,500 for 32 O and early B stars sufferingfrom a reddening between E_B-V_=0.06 and 1.57. The data have been usedto search for and calibrate a relation between equivalent width andreddening. When the interstellar lines show a single and sharpcomponent, useful relations to estimate reddening from equivalent widthshave been derived. The relation for Na I is most sensitive in the range0.0<=E_B-V_<=0.4, and the one for K I takes over at higherreddening. Good quality equivalent width measurements allow E_B-V_ to beestimated with an accuracy of about 0.05 mag. For multi-componentprofiles of Na I and K I lines the estimate of reddening is moreambiguous with a general scatter of 0.15mag. Close blends of multiplecomponents allow only an estimate of an upper limit to E_B-V_.
| Catalogue of stars in the northern Milky Way having H-alpha in emission
Not Available
| Optical and 21-cm observations of high-velocity gas towards subdwarfs in the halo and early-type stars in the disk
We present a study of high-velocity gas in the direction of 13 halosub-dwarfs located at absolute value of z approximately equals 0.5-2 kpcand of 8 early-type stars in the Galactic disk at d approximately equals1-4 kpc. For each line of sight of our sample we collected Ca II and NaI absorption spectra with the 2.5-m Isaac Newton Telescope at La Palma(Spain) and H I 21-cm emission profiles with the 100-m radiotelescope atEffelsberg (Germany). The faint sub-dwarfs (mv approximatelyequals 11-14) are observed for the first time at relatively highspectral resolution (approximately equals 25-30 km/s) in the optical. Bycomparing the optical absorptions (or upper limits) with the 21-cmemissions, we constrain the distances to the concentrations of neutralgas at high velocity named Complex C, Complex H, and for high velocitygas located between the Cohen Stream and the Magellanic Stream. We findnew evidence for gas at intermediate velocity in the halo and in thedisk of our Galaxy.
| Intrinsic colour indices of O- and B- type stars in the Vilnius photometric system.
Not Available
| SAO stars with infrared excess in the IRAS Point Source Catalog
We have undertaken a search for SAO stars with infrared excess in theIRAS Point Source Catalog. In contrast to previous searches, the entireIRAS (12)-(25)-(60) color-color diagram was used. This selection yieldeda sample of 462 stars, of which a significant number are stars withcircumstellar material. The stars selected can be identified aspre-main-sequence stars, Be stars, protoplanetary systems, post-AGBstars, etc. A number of objects are (visual) binary stars.Characteristic temperatures and IR excesses are calculated and theirrelations to spectral type are investigated.
| Photoelectric photometry of OB stars in the Vilnius system
Not Available
| Distribution and motions of OB stars in the direction of H and KHI Perseus.
Not Available
| An optical spiral arm beyond the Perseus arm
In the second galactic quadrant, optical spiral arm tracers have beencollected in a systematic literature search. A uniform reduction of thedata led to the detection of a distinct structure (probably a spiralarm) beyond the Perseus arm that is separated by a statisticallysignificant gap from the latter.
| Miscellaneous spectroscopic notes
Results of slit-spectrograph observations are reported for approximately260 stars. The data presented range from recognition of many new Ap, Am,and other unusual stars to H-alpha observations of early-typesupergiants and Be stars. The material discussed was obtained over thepast 40 years at a number of U.S. observatories and at the DominionAstrophysical Observatory in Victoria, B.C.
| Catalog of BV magnitudes and spectral classes of 6000 stars
The present catalog, compiled at the Abastumani Observatory, contains BVmagnitudes and spectral classes of about 6000 stars up to V(lim) = 13.0min five circular areas of 18 sq deg located near the salactic-equatorplane. The catalog is intended for star-statistics studies ofstar-formation regions.
| A library of stellar spectra
Spectra for 161 stars having spectral classes O-M and luminosity classesV, III, and I have been incorporated into a library available onmagnetic tape. The spectra extend from 3510 to 7427 A at a resolution ofabout 4.5 A. The typical photometric uncertainty of each resolutionelement in the spectra is on the order of 1 percent while broad-bandvariations are smaller than 3 percent. Potential uses for the libraryinclude population synthesis of galaxies and clusters, tests of stellaratmosphere models, spectral classification, and the generation of colorindices having arbitrary wavelength and bandpass.
| A survey of interstellar neutral potassium. I - Abundances and physical conditions in clouds toward 188 early-type stars
Observations of interstellar absorption in the resonance doublet 7664,7698 A of neutral potassium toward 188 early-type stars at a spectralresolution of 8 km/s are reported. The 7664 A line is successfullyseparated from nearly coincident telluric O2 absorption for all but afew of the 165 stars for which K I absorption is detected, makingpossible an abundance analysis by the doublet ratio method. Therelationships between the potassium abundances and other atomicabundances, the abundance of molecular hydrogen, and interstellarreddening are investigated.
| A spectrophotometric survey of stars along the Milky Way. IV
In the present paper a catalogue of spectrophotometric quantities,spectral types, monochromatic magnitudes and colour equivalents is givenfor all stars brighter than the magnitude m4400 = 10.5 in aregion of the Milky Way in Perseus. No absorption is found for starscloser than about r = 100 pc. The absorbing clouds are situated atdistances closer than 1 kpc and at about 2.5 kpc in the local arm andthe Perseus arm, respectively. The space between the two arms is freefrom absorption. It is also concluded that the Perseus arm continuesbeyond l = 140 deg, containing not only hydrogen gas but also dust to atleast l = 150 deg), while the content of OB stars decreases abruptly atl = 140 deg.
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | קאסיופיאה |
| התרוממות ימנית: | 02h11m43.91s |
| סירוב: | +60°42'44.5" |
| גודל גלוי: | 8.654 |
| מרחק: | 10000000 פארסק |
| תנועה נכונה: | 1 |
| תנועה נכונה: | -0.5 |
| B-T magnitude: | 9.989 |
| V-T magnitude: | 8.765 |
קטלוגים וכינוים:
|
