Contents
Images
Upload your image
DSS Images Other Images
Related articles
Search for C2- in Diffuse Clouds
A search has been carried out for the C2- ion indiffuse clouds toward HD 23180, HD 24912, HD 24398, HD 46711, and HD50064 using the HIDES spectrometer on the Okayama 188-cm telescope. Anupper limit of 8.3 × 1010, 1.8 × 1012cm-2 was obtained for the C2- columndensity. The upper limit value (3.8 × 1011cm-2) toward HD 23180 is two orders of magnitude smaller thanthat of the C2 radical. Possible production mechanisms forC2- are discussed.
| High-Resolution Observations of Interstellar Ca I Absorption-Implications for Depletions and Electron Densities in Diffuse Clouds
We present high-resolution (FWHM~0.3-1.5 km s-1) spectra,obtained with the AAT UHRF, the McDonald Observatory 2.7 m coudéspectrograph, and/or the KPNO coudé feed, of interstellar Ca Iabsorption toward 30 Galactic stars. Comparisons of the column densitiesof Ca I, Ca II, K I, and other species-for individual componentsidentified in the line profiles and also when integrated over entirelines of sight-yield information on relative electron densities anddepletions (dependent on assumptions regarding the ionizationequilibrium). There is no obvious relationship between the ratio N(CaI)/N(Ca II) [equal to ne/(Γ/αr) forphotoionization equilibrium] and the fraction of hydrogen in molecularform f(H2) (often taken to be indicative of the local densitynH). For a smaller sample of sight lines for which thethermal pressure (nHT) and local density can be estimated viaanalysis of the C I fine-structure excitation, the average electrondensity inferred from C, Na, and K (assuming photoionizationequilibrium) seems to be independent of nH andnHT. While the electron density (ne) obtained fromthe ratio N(Ca I)/N(Ca II) is often significantly higher than the valuesderived from other elements, the patterns of relative nederived from different elements show both similarities and differencesfor different lines of sight-suggesting that additional processesbesides photoionization and radiative recombination commonly andsignificantly affect the ionization balance of heavy elements in diffuseinterstellar clouds. Such additional processes may also contribute tothe (apparently) larger than expected fractional ionizations(ne/nH) found for some lines of sight withindependent determinations of nH. In general, inclusion of``grain-assisted'' recombination does reduce the inferred ne,but it does not reconcile the ne estimated from differentelements; it may, however, suggest some dependence of ne onnH. The depletion of calcium may have a much weakerdependence on density than was suggested by earlier comparisons with CHand CN. Two appendices present similar high-resolution spectra of Fe Ifor a few stars and give a compilation of column density data for Ca I,Ca II, Fe I, and S I.
| Some Diffuse Interstellar Bands Related to Interstellar C2 Molecules
We have investigated the correlations between the equivalent widths of21 selected diffuse interstellar bands (DIBs) and the correspondinginterstellar column densities N(C2), N(CN), and N(CH), toward53 stars with color excesses 0.11<=E(B-V)<=1.99. The observationaldata were derived primarily from echelle spectra acquired at R=38,000 aspart of our extensive, continuing survey of the bands. All but six ofthe 53 final spectra show signal-to-noise ratios >=800 at 5780Å. The principal result presented here is that seven of the 21bands prove to be examples of ``the C2 DIBs,'' a class ofweak, narrow bands whose normalized equivalent widthsWλ(X)/Wλ (λ6196) are wellcorrelated specifically with N(C2)/E(B-V) via power laws. Incontrast, the similarly normalized equivalent widths of the 14 other,well-known DIBs analyzed here are uncorrelated, or weaklyanticorrelated, with N(C2)/E(B-V), to within theobservational uncertainties. Thus, the polyatomic molecule(s) presumedto cause these seven C2 DIBs may bear a direct chemicalrelation to C2 that is not shared by the polyatomic moleculesputatively responsible for the other 14 bands. The C2 DIBsalso show positive correlations with N(CN)/E(B-V) and N(CH)/E(B-V) inour particular sample of light paths, although generally with shallowerslopes in the case of N(CN) and with greater scatter in the case ofN(CH). Eleven additional C2 DIBs are also identified but arenot analyzed here. Among the 18 C2 DIBs identified, fourapparently have not been previously detected. The λ4963 band isgenerally the strongest of the 18 C2 DIBs, while theλ4734 band shows the most sensitive correlation withN(C2).Based on observations obtained with the Apache Point Observatory 3.5 mtelescope, which is owned and operated by the Astrophysical ResearchConsortium.
| Observations of C3 in Translucent Sight Lines
The A1Πu<--X1Σ+g transition of the simplestpolyatomic carbon chain molecule, C3, at 4051.6 Å hasbeen searched for toward reddened stars where abundant C2 hadbeen reported and toward other stars with high color excess. Absorptionfrom C3 has been detected toward 15 stars with color excessE(B-V) from 0.33 to 1.12. The observed C3 column densities,ranging from 1012 to 1013 cm-2, arewell correlated with the corresponding C2 column densities,with N(C2)/N(C3)~40, indicating their closechemical relation. The carbon-rich sight line toward HD 204827 (forwhich no previous C2 observation had been reported) has byfar the highest C3 and C2 column densities. Thechemistry of formation of C3 from C2 is discussed.A search for the next strongest 020-000 vibronic band was unsuccessfulas a result of the low Franck-Condon factor and interference with astellar line. Searches for C4 and C5 werenegative.
| The total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
| Rejection of the C-7 Diffuse Interstellar Band Hypothesis
Using the new high-resolution (~8 km s-1) echellespectrograph on the 3.5 m telescope at the Apache Point Observatory, wehave begun a high-sensitivity survey of the diffuse interstellar bands(DIBs) in a large sample of reddened stars. Now that we are 2 years intothis long-term survey, our sample includes over 20 reddened stars thatshow at least one of the DIBs that had been suggested to be caused byC-7, based on the gas-phase measurement of theC-7 spectrum by J. P. Maier's group. Thehigh-quality astronomical data from this larger sample of stars, alongwith the spectroscopic constants from the new laboratory work recentlyreported by Maier's group, have enabled us to examine more carefully theagreement between C-7 and the DIBs. We find thatnone of the C-7 bands match the DIBs in wavelengthor expected profile. One of the DIBs (λ5748) attributed toC-7 is actually a stellar line. The two strongestDIBs attributed to C-7 (λ6270 andλ4964) are not correlated in strength, so they cannot share thesame carrier. On the whole, we find no evidence supporting thehypothesis that C-7 is a carrier of the DIBs.
| Observations of Diffuse Interstellar Bands Attributed to C-7
Recent advances in laboratory gas-phase spectroscopy of large moleculesand their ions permit a direct comparison between the diffuseinterstellar bands (DIBs) and proposed carriers. On the basis ofgas-phase data, Tulej et al. recently suggested that fiveA2Πu<--X2Πgelectronic transitions of the linear carbon-chain anionC-7 match with DIBs. We have obtainedhigh-resolution visible spectra of four reddened stars (HD 46711, HD50064, HD 183143, and Cyg OB2 12) to make a detailed comparison with theC-7 laboratory data. Our data show that three ofthe C-7 bands (000 at 6270.2Å, 310 at 6064.0 Å, and120310 at 4963.0 Å)are in good agreement with DIBs in wavelength and relative intensity. Afourth band (110 at 5612.8 Å) also agrees inintensity but is apparently off by 2 Å in wavelength. All otherlaboratory bands of C-7 are not expected to bedetectable in astronomical spectra with the current level ofsensitivity. The gas-phase spectrum of C-7 agreeswith the DIBs better than that of any previously proposed molecule.However, the question of whether C-7 is a DIBcarrier cannot be definitively answered until (1) better laboratorymeasurements confirm, refute, or explain the wavelength discrepancy forthe 110 band and/or (2) better astronomicalspectra reveal the presence or absence of otherC-7 bands. Based on observations obtained with theApache Point Observatory 3.5 m telescope, which is owned and operated bythe Astrophysical Research Consortium.
| Laser Spectroscopy of the Carbon Chains HC_7H and HC_9H
Strong vibronic bands of the ^3Sigma^-_u<--X^3Sigma^-_g transition ofthe linear triplet radicals HC_7H and HC_9H have been measured in thegas phase by cavity ringdown spectroscopy. The origin band of HC_7H andthe origin and nu_3 bands of HC_9H all exhibit well resolved P and Rbranches. For HC_9H, the origin band is within 1 Å of the diffuseinterstellar band lambda5818, yet insufficiently close for positiveidentification. In both molecules, internal conversion is much morerapid than radiative emission, and fluorescence is not observed. Lowerlimits on the radiationless lifetime of the upper state of the originband are determined to be 0.1 ns for HC_7H and 0.01 ns for HC_9H.Because the origin bands of these two radicals are about equallyintense, it should be possible to detect longer members of the series inthe gas phase.
| 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.
| New Perspectives on AX Monocerotis
AX Moncerotis is a 232d, noneclipsing, interacting binary star thatconsists of a K giant, a Be-like giant, and large amounts ofcircumstellar material. The K star is almost certainly a synchronousrotator and is probably in contact with its critical lobe. The Be starwas believed to be a rapid rotator based on extremely wide absorptionlines, but new spectra show that these lines arise from thecircumstellar environment. Hydrogen emission, also circumstellar, ismany times stronger than the continuum. Near-ultraviolet light curvesexhibit a 0.5 mag dip near phase 0.75, but there is no such variabilityat longer wavelengths. Gas flow trajectories from the cusp of the K startoward the Be star provide a simple explanation for the photometric andspectroscopic behavior. We may have found a decreasing orbital period,but more data are necessary to confirm this result. We present severalmodels for AX Mon based on (1) new and archival visible photometry, (2)archival ultraviolet spectroscopy, (3) new and archival visiblespectroscopy, (4) new visible polarimetry, and (5) new radio photometry.Future observations, including optical interferometry, are proposed.
| 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.
| Has interstellar forbidden Fe X been detected in the spectrum of SN 1987 A?
The detection of forbidden Fe X is found to be inconsistent with the lowlevels of diffuse X-ray flux identified with the Einstein and RosatX-ray satellites. The observed line can be interpreted as the slightlyredshifted wavelength 6379.3 of the diffuse interstellar band, in whichcase the velocity would equal that of the strong interstellar atomiclines in the spectrum of SN 1987 A. The unique feature is interpreted tobe evidence of variations in the ratios of interstellar lines forabsorbing clouds.
| Hydrogenated amorphous carbon-coated silicate particles as a source of interstellar extinction
A new model for interstellar grains has recently been proposed in whichlarge and small silicate grains are mantled with thin layers ofhydrogenated amorphous carbon (HAC or a-C:H) and amorphous carbon (a-C).A complete description of the grain model is presented for the firsttime. The optical properties of small inhomogenous particles arediscussed and new expressions for carbon depletion, bump strength andalbedo are derived. It is shown, in particular, that the wide variety ofinterstellar extinction curves can be explained by variations in carbondepletion, and model fits to normal and extreme cases of extinction arepresented. The model enables a direct measurement of carbon depletion tobe made from the extinction data and implies that carbon depletion in aninterstellar cloud is determined by the recent history of that cloud.Thus, on this model, grains respond to and react with their environment,rather than being immutable, inert entities in the interstellar gas.
| The interstellar 217 NM band - A third catalogue of equivalent widths
A catalog of equivalent widths of the 217 nm interstellar absorptionband as well as other parameters characterizing the extinction curve inthe ultraviolet has been compiled for 790 O and B stars. A relativelytight correlation between the equivalent width of the 217 nm band andE(B-V) indicates that the absorber of this band is connected with thepopulation of larger interstellar grains responsible for the visualextinction. The parameter characterizing the amount of extinction in thefar UV is only weakly correlated with E(B-V), a result in accord withthe assumption that a second population of very small grains causes therapid increase of the far-UV extinction.
| 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.
| The variation of galactic interstellar extinction in the ultraviolet
It has been found that the wavelength dependence of interstellarextinction is not the same for all stars in the Galaxy. The presentinvestigation is concerned with a further demonstration of the degree ofvariation of interstellar extinction in the UV, taking into account newextinction measurements toward 29 early-type stars. The stars do notrepresent a random sample. Approximately 15 of them were chosen becausethey have either an unusually large or an unusually small ratio of thestrength of the diffuse interstellar band at 4430 A to the color excessE(B-V). Five stars have a ratio of these quantities near average andnine additional stars are illuminating reflection nebulae. Attention isgiven to the deviation from the average galactic extinction law, denseversus diffuse cloud environments, and the galactic longitudedependence.
| Ultraviolet extinction and diffuse band strength correlations
Correlations between UV extinction parameters and diffuse band strengthsare south, using a data base of 50 stars with recently measuredextinction curves. A novel aspect of this study is that the basicdependence of most interstellar parameters on E(B-V) (or, nearlyequivalently, on the total hydrogen column density) has been largelycanceled out. After this cancellation, a weak correlation is foundbetween the 4430 A diffuse band and the 2175 A extinction feature. Noother correlations are found. These results support a molecular originfor the 5780 A and 6284 A bands. It is speculated that the correlationpattern found for the 4430 A band can be explained if this bandoriginates in reactions on disordered grain surfaces.
| New UBVRI photometry for 900 supergiants
A description is presented of the results obtained in connection with asystematic program of supergiant photometry on the Johnson UBVRI system.During the eight years after the start of the program, almost 1000 starshave been observed, about 400 three or more times each. The originalselection of stars used the spectral type catalog of Jaschek et al.(1964) to choose supergiants. Since observations were possible from bothChile and Canada, no declination limits were imposed, and no particularselection criteria were imposed other than to eliminate carbon stars.These are so red as to require enormous extrapolations of thetransformation equations.
| Shock processing of interstellar grains
Theoretical and observational evidence is presented that shockprocessing of interstellar dust grains by supernova blast waves affectsboth heavy element depletions and ultraviolet extinction curves. Bycoupling a realistic model of grain sizes and populations with aradiative shock code, significant grain destruction at velocities as lowas 40 km/s is demonstrated. Nonthermal sputtering and grain-graincollisions destroy relatively more large grains than small, and moresilicates than graphite. Consequently, both the 2175 A extinction 'bump'and the far-ultraviolet normalized extinction are increased in strength.Ultraviolet extinction studies with the International UltravioletExplorer of nine stars near three supernova remnants (the MonocerosLoop, Shajn 147, and Vela) exhibit strong 2175 A bumps and normal orhigh far-ultraviolet extinction. Diffuse bands, if they are created bysmall grains, should show little correlation with such activity.
| Infrared photometry of early-type stars. I
K (2.2-micron) magnitudes are given for reddened early-type stars in thegalactic anticenter region between galactic longitudes of 160 and 230deg, in conjunction with ultraviolet photometry from the TD1 satellite.A value of 3.12 + or - 0.05 for the extinction ratio R is derived forthe general field and for the Mon OB2 region. The strength of theinterstellar absorption feature at 2200 A is calibrated in terms oftotal visual extinction. Many of the emission-line stars show infraredexcess, and there are indications that in some of these the 2200-Aabsorption is depleted.
| Studies of luminous stars in nearby galaxies. I. Supergiants and O stars in the Milky Way.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978ApJS...38..309H&db_key=AST
| Observations in linearly polarized light of the intensity of the diffuse lam 6180 absorption band in 56 southern O, B and A stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&A....70..195G&db_key=AST
| The value of R in Monoceros
Recent photometric and spectroscopic observations are used inconjunction with other data for early-type stars in northern Monocerosin order to investigate the local value of R (the ratio of total toselective extinction). From a variable-extinction analysis, it isconcluded that a ratio of approximately 3.2 is appropriate for thegeneral interstellar extinction in this region and that there is noevidence here for the existence of local anomalies. The two majorassociations Mon OB 1 and Mon OB 2 are clearly delineated and are foundto exhibit properties typical of such young stellar groups. Derivedproperties for a few interesting stars are presented.
| Equivalent widths and rotational velocities of southern early-type stars
Not Available
| Observations of the diffuse 4430 A absorption band in southern O, B, and A stars
Photoelectric narrow-band observations of the intensity of the diffuseinterstellar 4430 A absorption band have been carried out for 65southern O, B and A stars of luminosity classes I and II. The dependenceof the 4430 A index on stellar spectral lines is eliminated and thevariation of the ratio Jc/E(B-V) of 4430-A wavelength to selectiveabsorption from place to place in the Galaxy is discussed. It is foundthat Jc/E(B-V) is significantly lower in the inter-arm region frominside the inner and outer spiral arms. The observed value of Jc/E(B-V)for HD 153919, the optical component of the binary system containing theX-ray source 2 U 1700-37, indicates a distance of at least 1.5 kpc whichsuggests that it is more luminous and massive than an ordinary O 6 star.
| On the kinematical and spatial coincidence of optical and radio spiral arms in our galaxy.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973A&A....24..393M&db_key=AST
| A Test for Relative Motions of Gas and Young Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972PASP...84..273M&db_key=AST
| Interstellar extinction anomalies and the diffuse interstellar bands.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74.1061W&db_key=AST
| Observations of interstellar reddening V,
Not Available
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Monoceros |
| Right ascension: | 06h34m57.05s |
| Declination: | +02°45'43.2" |
| Apparent magnitude: | 9.077 |
| Proper motion RA: | -3.4 |
| Proper motion Dec: | -1.1 |
| B-T magnitude: | 10.027 |
| V-T magnitude: | 9.156 |
Catalogs and designations:
|
