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Blueshifted diffuse interstellar bands in the spectrum of HD 34078
In this paper, we report the very first observation of diffuseinterstellar bands (DIBs) that, in the spectrum of HD 34078 (AE Aur),are blueshifted with respect to the normal position that they have inother objects, where the rest-wavelength velocity frame is determinedusing very sharp interstellar atomic lines or molecular features. Onlyreasonably narrow DIBs seemingly show this effect, which is absent inbroader ones. The result is confirmed independently using threedifferent spectrographs attached to two different telescopes.
| 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.
| Astrophysics in 2004
In this 14th edition of ApXX,1 we bring you the Sun (§ 2) and Stars(§ 4), the Moon and Planets (§ 3), a truly binary pulsar(§ 5), a kinematic apology (§ 6), the whole universe(§§ 7 and 8), reconsideration of old settled (§ 9) andunsettled (§ 10) issues, and some things that happen only on Earth,some indeed only in these reviews (§§ 10 and 11).
| Wolf-Rayet and O star runaway populations from supernovae
We present numerical simulations of the runaway fractions expectedamongst O and Wolf-Rayet star populations resulting from stars ejectedfrom binaries by the supernova of the companion. Observationally, therunaway fraction for both types of star is similar, prompting theexplanation that close dynamical interactions are the main cause ofthese high-velocity stars. We show that, provided that the initialbinary fraction is high, a scenario in which two-thirds of massiverunaways are from supernovae is consistent with these observations. Ourmodels also predict a low frequency of runaways with neutron starcompanions and a very low fraction of observable Wolf-Rayet-compactcompanion systems.
| Evolution of X-ray emission from young massive star clusters
The evolution of X-ray emission from young massive star clusters ismodelled, taking into account the emission from the stars as well asfrom the cluster wind. It is shown that the level and character of thesoft (0.2-10 keV) X-ray emission change drastically with cluster age andare tightly linked with stellar evolution. Using the modern X-rayobservations of massive stars, we show that the correlation betweenbolometric and X-ray luminosity known for single O stars also holds forO+O and (Wolf-Rayet) WR+O binaries. The diffuse emission originates fromthe cluster wind heated by the kinetic energy of stellar winds andsupernova explosions. To model the evolution of the cluster wind, themass and energy yields from a population synthesis are used as input toa hydrodynamic model. It is shown that in a very young cluster theemission from the cluster wind is low. When the cluster evolves, WRstars are formed. Their strong stellar winds power an increasing X-rayemission of the cluster wind. Subsequent supernova explosions pump thelevel of diffuse emission even higher. Clusters at this evolutionarystage may have no X-ray-bright stellar point sources, but a relativelyhigh level of diffuse emission. A supernova remnant may become adominant X-ray source, but only for a short time interval of a fewthousand years. We retrieve and analyse Chandra and XMM-Newtonobservations of six massive star clusters located in the LargeMagellanic Cloud (LMC). Our model reproduces the observed diffuse andpoint-source emission from these LMC clusters, as well as from theGalactic clusters Arches, Quintuplet and NGC 3603.
| Correlation patterns between 11 diffuse interstellar bands and ultraviolet extinction
We relate the equivalent widths of 11 diffuse interstellar bands,measured in the spectra of 49 stars, to different colour excesses in theultraviolet. We find that most of the observed bands correlatepositively with the extinction in the neighbourhood of the2175-Åbump. Correlation with colour excesses in other parts of theextinction curve is more variable from one diffuse interstellar band toanother; we find that some diffuse bands (5797, 5850 and 6376 Å)correlate positively with the overall slope of the extinction curve,while others (5780 and 6284 Å) exhibit negative correlation. Wediscuss the implications of these results on the links between thediffuse interstellar band carriers and the properties of theinterstellar grains.
| The chemistry of transient microstructure in the diffuse interstellar medium
Transient microstructure in the diffuse interstellar medium (ISM) hasbeen observed towards Galactic and extragalactic sources for decades,usually in lines of atoms and ions, and, more recently, in molecularlines. Evidently, there is a molecular component to the transientmicrostructure. In this paper, we explore the chemistry that may arisein such microstructure. We use a photodissociation region (PDR) code tomodel the conditions of relatively high density, low temperature, verylow visual extinction and very short elapsed time that are appropriatefor these objects. We find that there is a well-defined region ofparameter space where detectable abundances of molecular species mightbe found. The best matching models are those where the interstellarmicrostructure is young (<100 yr), small (~100 au) and dense(>104 cm-3).
| Profiles of Very Weak Diffuse Interstellar Bands around 6440 Å
Profiles of very weak diffuse interstellar bands (DIBs) between 6400 and6470 Å observed with high resolution and very high S/N aredemonstrated. We show that with the increasing quality of reddenedstellar spectra, the whole spectral range is covered with weak or veryweak DIBs-at least one every 2-3 Å. We also present the details ofthe profiles of a few stronger features; the presence of substructuresresembles the profiles of strong DIBs observed in high resolution duringthe last decade and supports the hypothesis of a molecular origin of atleast a majority of DIBs.
| Low-Mass Runaway Stars from the Orion Trapezium Cluster
In the course of a search for common proper-motion binaries in the Jones& Walker (JW) catalog of proper motions in the Orion Nebula Cluster,we came across several faint stars with proper motions larger than 1"per century and probabilities of membership P larger than 0.90. Suchstars are interesting because they could be low-mass runaway starsrecently accelerated by n-body interactions in compact multiple systems.Of particular interest among these stars is JW 451, which has a P =0.98, the largest transverse velocity among all the stars with P>=0.5( 69+/-38 km s-1), and a proper-motion vector suggesting thatit was accelerated by the θ1 Orionis C triple systemsome 1000 years ago. A closer examination of those JW stars withμ>1'' per century revealed that two other stars, JW 349and JW 355 (with transverse velocities of 38+/-9 and 90+/-9 kms-1, respectively), in spite of being listed with P = 0 byJW, should also be considered part of the cluster, because these objectsare also externally ionized proplyds. In fact, Hillenbrand assigns tothem probabilities of membership of 0.99. Moreover, the proper-motionerrors of these two stars are relatively small, and so they are goodcandidates to be runaway stars recently accelerated in the Orion NebulaCluster.
| X-Ray Counterparts of Runaway Stars
An X-ray search for possible compact companions of runaway OB stars hasbeen conducted using pointed ROSAT observations. Of a list of 71 runawaystars, ROSAT exposures were available for 24, of which 13 are detected.These numbers are nearly 3 times larger than for a previously studiedEinstein sample, and spectral information is exploited as well.Luminosities, hardness ratios, and long-term variability are as fornormal OB stars and do not suggest the presence of collapsed companions.A result like this is often interpreted as support for dynamicalejection from a dense group rather than a supernova event in a binary asa production process for runaway stars. There are, however, severalcircumstances that may adversely affect the observability of a compactcompanion, or after a supernova explosion systems may be disruptedbecause of the large natal kick velocity imparted to the neutron star asa result of asymmetries in the explosions. It is noted that there isactually evidence for both of these production routes and that they maybe expected to occur sequentially in the evolution of OB associations.
| Deep Imaging Surveys of Star-forming Clouds. III. Herbig-Haro Objects in the Perseus Molecular Cloud
We present a catalog of 72 new Herbig-Haro (HH) objects discovered inthe Perseus molecular cloud. There are 69 previously cataloged HHobjects in this region, and the new discoveries bring the total numberof known HH objects in Perseus to 141. Individual outflows often containseveral distinct HH objects. These observations demonstrate that thePerseus molecular cloud is one of the most active star-forming regionsin the solar vicinity. We explore different methods for probing themomentum injection rate of outflows and examine whether outflows candrive turbulence within the molecular cloud. On the scale of the entirePerseus cloud, the shocks produced by outflows from young stars may notinject momentum at a sufficient rate to counter the rate at whichmomentum decays. However, intense outflow activity within individualcloud cores with high star formation rates, such as NGC 1333, may besufficient to locally support or even disrupt the core.
| The Birth of High-Mass Stars: Accretion and/or Mergers?
The observational consequences of the merger scenario for massive starformation are explored and contrasted with the gradual accumulation ofmass by accretion. In high-density protostar clusters, envelopes anddisks provide a viscous medium that can dissipate the kinetic energy ofpassing stars, greatly enhancing the probability of capture.Protostellar mergers may produce high-luminosity infrared flares lastingyears to centuries followed by a luminosity decline on theKelvin-Helmholtz timescale of the merger product. Mergers may besurrounded by thick tori of expanding debris, impulsive wide-angleoutflows, and shock-induced maser and radio continuum emission.Collision products are expected to have fast stellar rotation and alarge multiplicity fraction. Close encounters or mergers will producecircumstellar debris disks with an orientation that differs from that ofa preexisting disk. Thus, massive stars growing by a series of mergersmay produce eruptive outflows with random orientations; the walls of theresulting outflow cavities may be observable as filaments of dense gasand dust pointing away from the massive star. The extremely rare mergerof two stars close to the upper-mass end of the initial mass functionmay be a possible pathway to hypernova-generated gamma-ray bursts. Incontrast with the violence of merging, the gradual growth of massivestars by accretion is likely to produce less infrared variability,relatively thin circumstellar accretion disks that maintain theirorientation, and collimated bipolar outflows that are scaled-up versionsof those produced by low-mass young stellar objects. While suchaccretional growth can lead to the formation of massive stars inisolation or in loose clusters, mergers can only occur in high-densitycluster environments. It is proposed that the outflow emerging from theOMC-1 core in the Orion molecular cloud was produced by a protostellarmerger that released between 1048 and 1049 ergsless than a thousand years ago.
| Chemical composition of Galactic OB stars. II. The fast rotator ζ Ophiuchi
ζ Oph, HD 149757, is an O9.5Vnn star with a very high projected rotational velocity (v sin i ≥340 km s-1). It is also a classical runaway star due to itshigh proper motion. We perform a quantitative analysis of its opticalspectrum in order to measure important observables of the star such asits mass, effective temperature, luminosity and He, C, N, and Oabundances. Comparing these observed values to those predicted by therotating evolutionary models of the Geneva group we find that none ofthe two sets of models (those of 2000 and 2003) is capable ofreproducing the characteristics of the star. Nevertheless, due to itsrunaway nature, the reason for this discrepancy may be that the star isnot the result of the evolution of a single object, but the product ofthe evolution of a close binary system.
| O stars with weak winds: the Galactic case
We study the stellar and wind properties of a sample of Galactic Odwarfs to track the conditions under which weak winds (i.e. mass lossrates lower than 10-8 Mȯ yr-1)appear. The sample is composed of low and high luminosity dwarfsincluding Vz stars and stars known to display qualitatively weak winds.Atmosphere models including non-LTE treatment, spherical expansion andline blanketing are computed with the code CMFGEN (Hillier & Miller1998, ApJ, 496, 407). Both UV and Hα lines are used to derive windproperties while optical H and He lines give the stellar parameters. Wefind that the stars of our sample are usually 1 to 4 Myr old. Mass lossrates of all stars are found to be lower than expected from thehydrodynamical predictions of Vink et al. (2001, A&A, 369, 574). Forstars with log {L}/{Lȯ} 5.2, the reduction is byless than a factor 5 and is mainly due to the inclusion of clumping inthe models. For stars with log {L}/{Lȯ} 5.2 thereduction can be as high as a factor 100. The inclusion of X-rayemission (possibly due to magnetic mechanisms) in models with lowdensity is crucial to derive accurate mass loss rates from UV lines,while it is found to be unimportant for high density winds. The modifiedwind momentum - luminosity relation shows a significant change of slopearound this transition luminosity. Terminal velocities of low luminositystars are also found to be low. Both mass loss rates and terminalvelocities of low L stars are consistent with a reduced line forceparameter α. However, the physical reason for such a reduction isstill not clear although the finding of weak winds in Galactic starsexcludes the role of a reduced metallicity. There may be a link betweenan early evolutionary state and a weak wind, but this has to beconfirmed by further studies of Vz stars. X-rays, through the change inthe ionisation structure they imply, may be at the origin of a reductionof the radiative acceleration, leading to lower mass loss rates. Abetter understanding of the origin of X-rays is of crucial importancefor the study of the physics of weak winds.
| To see or not to see a bow shock. Identifying bow shocks with Hα allsky surveys
OB-stars have the highest luminosities and strongest stellar winds ofall stars, which enables them to interact strongly with theirsurrounding ISM, thus creating bow shocks. These offer us an idealopportunity to learn more about the ISM. They were first detected andanalysed around runaway OB-stars using the IRAS allsky survey by vanBuren et al. (1995, AJ, 110, 2614). Using the geometry of such bowshocks information concerning the ISM density and its fluctuations canbe gained from such infrared observations. As to help to improve the bowshock models, additional observations at other wavelengths, e.g.Hα, are most welcome. However due to their low velocity these bowshocks have a size of 1°, and could only be observed as awhole with great difficulties. In the light of the new Hα allskysurveys (SHASSA/VTSS) this is no problem any more. We developeddifferent methods to detect bow shocks, e.g. the improved determinationof their symmetry axis with radial distance profiles. Using twoHα-allsky surveys (SHASSA/VTSS), we searched for bow shocks andcompared the different methods. From our sample we conclude, that thecorrelation between the direction of both proper motion and the symmetryaxis determined with radial distance profile is the most promisingdetection method. We found eight bow shocks around HD17505, HD 24430, HD48099, HD 57061, HD92206, HD 135240, HD149757, and HD 158186 from 37 candidatestaken from van Buren et al. (1995, AJ, 110, 2614). Additionally to thetraditional determination of ISM parameters using the standoff distanceof the bow shock, another approach was chosen, using the thickness ofthe bow-shock layer. Both methods lead to the same results, yieldingdensities ( 1 cm-3) and the maximal temperatures (104 K), that fit well to the up-to-date picture of the WarmIonised Medium.
| New runaway OB stars with HIPPARCOS
A Monte Carlo method for detection of runaway OB stars fromobservational data is proposed. 61 runaway OB star candidates have beendetected by an analysis of Hipparcos proper motions. The peculiartangential and total transverse velocities have been determined forthese stars. A list of the detected runaway star candidates ispresented. The evidence of a discrepancy between photometric andparallactic distances of runaway OB star candidates is presented.
| A far UV study of interstellar gas towards HD 34078: High excitation H2 and small scale structure
To investigate the presence of small scale structure in the spatialdistribution of H2 molecules we have undertaken repeated FUSEUV observations of the runaway O9.5V star, HD 34078. In this paper wepresent five spectra obtained between January 2000 and October 2002.These observations reveal an unexpectedly large amount of highly excitedH2>. Column densities for H2 levels from (v =0, J = 0) up to (v = 0, J = 11) and for several v = 1 and v = 2 levelsare determined. These results are interpreted in the frame of a modelinvolving essentially two components: i) a foreground cloud (unaffectedby HD 34078) responsible for the H2 (J = 0, 1), CI, CH,CH+ and CO absorptions; ii) a dense layer of gas (n ≃104 cm-3) close to the O star and stronglyilluminated by its UV flux which accounts for the presence of highlyexcited H2. Our model successfully reproduces theH2 excitation, the CI fine-structure level populations aswell as the CH, CH+ and CO column densities. We also examinethe time variability of H2 absorption lines tracing each ofthese two components. From the stability of the J = 0, 1 and 2 dampedH2 profiles we infer a 3σ upper limit on column densityvariations Δ N(H2)/N(H2) of 5% over scalesranging from 5 to 50 AU. This result clearly rules out any pronouncedubiquitous small scale density structure of the kind apparently seen inHI. The lines from highly excited gas are also quite stable (equivalentto Δ N/N ≤30%) indicating i) that the ambient gas throughwhich HD 34078 is moving is relatively uniform and ii) that the gas flowalong the shocked layer is not subject to marked instabilities.Based on observations performed by the FUSE mission and at the CFHTtelescope.
| High-mass X-ray binaries and OB runaway stars
High-mass X-ray binaries (HMXBs) represent an important phase in theevolution of massive binary systems and provide fundamental informationon the properties of the OB-star primaries and their compact secondaries(neutron star, black hole). Recent observations indicate that theneutron stars in some of these systems (Vela X-1, 4U 1700-37) are moremassive than the canonical mass of 1.35 MMȯ. Theseobservations have important consequences for the equation of state atsupranuclear densities and the formation mechanism(s) of neutron starsand black holes: supernovae and gamma-ray bursts. As a consequence ofthe supernova explosion that produced the compact star in these systems,HMXBs have high space velocities and thus are runaways. Alternatively,OB-runaway stars can be ejected from a cluster through dynamicalinteractions. Observations obtained with the Hipparcos satelliteindicate that both scenarios are at work.
| N-body simulations of stars escaping from the Orion nebula
We study the dynamical interaction in which the two single runawaystars, AE Aurigæ and μ Columbæ, and the binary ιOrionis acquired their unusually high space velocity. The two singlerunaways move in almost opposite directions with a velocity greater than100 km s-1 away from the Trapezium cluster. The star ιOrionis is an eccentric (e~= 0.8) binary moving with a velocity of about10 km s-1 at almost right angles with respect to the twosingle stars. The kinematic properties of the system suggest that astrong dynamical encounter occurred in the Trapezium cluster about 2.5Myr ago. Curiously enough, the two binary components have similarspectral type but very different masses, indicating that their ages mustbe quite different. This observation leads to the hypothesis that anexchange interaction occurred in which an older star was swapped intothe original ι Orionis binary. We test this hypothesis by acombination of numerical and theoretical techniques, using N-bodysimulations to constrain the dynamical encounter, binary evolutioncalculations to constrain the high orbital eccentricity of ιOrionis and stellar evolution calculations to constrain the agediscrepancy of the two binary components. We find that an encounterbetween two low eccentricity (0.4 <~e<~ 0.6) binaries withcomparable binding energy, leading to an exchange and the ionization ofthe wider binary, provides a reasonable solution to this problem.
| A Galactic O Star Catalog
We have produced a catalog of 378 Galactic O stars with accuratespectral classifications that is complete for V<8 but includes manyfainter stars. The catalog provides cross-identifications with othersources; coordinates (obtained in most cases from Tycho-2 data);astrometric distances for 24 of the nearest stars; optical (Tycho-2,Johnson, and Strömgren) and NIR photometry; group membership,runaway character, and multiplicity information; and a Web-based versionwith links to on-line services.
| Effects of Metallicity on the Rotational Velocities of Massive Stars
Recent theoretical predictions for low-metallicity massive stars predictthat these stars should have drastically reduced equatorial winds (massloss) while on the main sequence, and so should retain most of theirangular momentum. Observations of both the Be/(B+Be) ratio and theblue-to-red supergiant ratio appear to have a metallicity dependencethat may be caused by high rotational velocities. We have analyzed 39archival Hubble Space Telescope Imaging Spectrograph (STIS),high-resolution, ultraviolet spectra of O-type stars in the MagellanicClouds to determine their projected rotational velocities Vsini. Ourmethodology is based on a previous study of the projected rotationalvelocities of Galactic O-type stars using International UltravioletExplorer (IUE) short-wavelength prime (SWP) camera high-dispersionspectra, which resulted in a catalog of Vsini values for 177 O-typestars. Here we present complementary Vsini values for 21 LargeMagellanic Cloud and 22 Small Magellanic Cloud O-type stars based onSTIS and IUE UV spectroscopy. The distribution of Vsini values forO-type stars in the Magellanic Clouds is compared to that of GalacticO-type stars. Despite the theoretical predictions and indirectobservational evidence for high rotation, the O-type stars in theMagellanic Clouds do not appear to rotate faster than their Galacticcounterparts.
| Rocket and Far Ultraviolet Spectroscopic Explorer Observations of IC 405: Differential Extinction and Fluorescent Molecular Hydrogen
We present far-ultraviolet spectroscopy of the emission/reflectionnebula IC 405 obtained by a rocket-borne long-slit spectrograph and theFar Ultraviolet Spectroscopic Explorer (FUSE). Both data sets show arise in the ratio of the nebular surface brightness to stellar flux(S/F*) of approximately 2 orders of magnitude toward the blueend of the far-UV bandpass. Scattering models using simple dustgeometries fail to reproduce the observed S/F* for realisticgrain properties. The high spectral resolution of the FUSE data revealsa rich fluorescent molecular hydrogen spectrum ~1000" north of the starthat is clearly distinguished from the steady blue continuum. TheS/F* remains roughly constant at all nebular pointings,showing that fluorescent molecular hydrogen is not the dominant cause ofthe blue rise. We discuss three possible mechanisms for the ``bluedust'': differential extinction of the dominant star (HD 34078), unusualdust-grain properties, and emission from nebular dust. We conclude thatuncertainties in the nebular geometry and the degree of dust clumpingare most likely responsible for the blue rise. As an interestingconsequence of this result, we consider how IC 405 would appear in aspatially unresolved observation. If IC 405 were observed with a spatialresolution of less than 0.4 pc, for example, an observer would infer afar-UV flux that was 2.5 times the true value, giving the appearance ofa stellar continuum that was less extinguished than radiation from thesurrounding nebula, an effect that is reminiscent of the observedultraviolet properties of starburst galaxies.
| New Runaway O-stars Based on Data from HIPPARCOS
12 new runaway O-stars are identified using an analysis of their propermotions based on data from HIPPARCOS. The peculiar tangential and totaltransverse velocities of these stars are determined. A list of theobserved runaway stars is given.
| Total to Selective Extinction Ratios and Visual Extinctions from Ultraviolet Data
We present determinations of the total to selective extinction ratio R_Vand visual extinction A_V values for Milky Way stars using ultravioletcolor excesses. We extend the analysis of Gnacinski and Sikorski (1999)by using non-equal weights derived from observational errors. We presenta detailed discussion of various statistical errors. In addition, weestimate the level of systematic errors by considering differentnormalization of the extinction curve adopted by Wegner (2002). Ourcatalog of 782 R_V and A_V values and their errors is available in theelectronic form on the World Wide Web.
| On the Hipparcos parallaxes of O stars
We compare the absolute visual magnitude of the majority of bright Ostars in the sky as predicted from their spectral type with the absolutemagnitude calculated from their apparent magnitude and the Hipparcosparallax. We find that many stars appear to be much fainter thanexpected, up to five magnitudes. We find no evidence for a correlationbetween magnitude differences and the stellar rotational velocity assuggested for OB stars by Lamers et al. (1997, A&A, 325, L25), whosesmall sample of stars is partly included in ours. Instead, by means of asimulation we show how these differences arise naturally from the largedistances at which O stars are located, and the level of precision ofthe parallax measurements achieved by Hipparcos. Straightforwardlyderiving a distance from the Hipparcos parallax yields reliable resultsfor one or two O stars only. We discuss several types of bias reportedin the literature in connection with parallax samples (Lutz-Kelker,Malmquist) and investigate how they affect the O star sample. Inaddition, we test three absolute magnitude calibrations from theliterature (Schmidt-Kaler et al. 1982, Landolt-Börnstein; Howarth& Prinja 1989, ApJS, 69, 527; Vacca et al. 1996, ApJ, 460, 914) andfind that they are consistent with the Hipparcos measurements. AlthoughO stars conform nicely to the simulation, we notice that some B stars inthe sample of \citeauthor{La97} have a magnitude difference larger thanexpected.
| Toward an adequate method to isolate spectroscopic families of diffuse interstellar bands
We divide some of the observed diffuse interstellar bands (DIBs) intofamilies that appear to have the spectral structure of single species.Three different methods are applied to separate such families, exploringthe best approach for future investigations of this type. Starting witha statistical treatment of the data, we found that statistical methodsby themselves give insufficient results. Two other methods of dataanalysis (`averaging equivalent widths' and `investigating the figureswith arranged spectrograms') were found to be more useful as tools forfinding the spectroscopic families of DIBs. On the basis of thesemethods, we suggest some candidates as `relatives' of 5780- and5797-Å bands.
| 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.
| The Massive Triple Star System HD 16429 A
HD 16429 A is a triple star system consisting of a single-linedspectroscopic binary and a widely separated third component, previouslyidentified via speckle interferometry. Here I present the first orbitalelements for the unblended spectroscopic binary as well as estimates ofthe spectral types and relative flux contributions for each visiblecomponent based on a Doppler tomographic reconstruction of theirspectra. There are several stars around HD 16429 A, including the nearbyBe X-ray binary and microquasar LS I +61deg303, which allprobably belong to a subcluster within the Cas OB6 association.
| Observations of Rotationally Resolved C3 in Translucent Sight Lines
The rotationally resolved spectrum of theA1Πu<--X1Σ+g000-000 transition of C3, centered at 4051.6 Å, hasbeen observed along 10 translucent lines of sight. To interpret thesespectra, a new method for the determination of column densities andanalysis of excitation profiles involving the simulation and fitting ofobserved spectra has been developed. The populations of lower rotationallevels (J<=14) in C3 are best fitted by thermaldistributions that are consistent with the kinetic temperaturesdetermined from the excitation profile of C2. Just as in thecase of C2, higher rotational levels (J>14) ofC3 show increased nonthermal population distributions inclouds that have been determined to have total gas densities below ~500cm-3.
| A Method for Simultaneous Determination of AV and R and Applications
A method for the simultaneous determination of the interstellarextinction (AV) and of the ratio of total to selectiveextinction (R), derived from the 1989 Cardelli, Clayton, & Mathisfitting of the interstellar extinction law, is presented and applied toa set of 1900 color excesses derived from observations of stars inUBVRIJHKL. The method is used to study the stability of AVand R within selected regions in Perseus, Scorpius, Monoceros, Orion,Sagittarius, Ophiuchus, Carina, and Serpens. Analysis shows that R isapproximately constant and peculiar to each sector, with mean valuesthat vary from 3.2 in Perseus to 5.6 in Ophiuchus. These results aresimilar to published values by Aiello et al., He et al., Vrba &Rydgren, O'Donnell, and Cardelli, Clayton, & Mathis.
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Osservazione e dati astrometrici
| Costellazione: | Auriga |
| Ascensione retta: | 05h16m18.20s |
| Declinazione: | +34°18'43.0" |
| Magnitudine apparente: | 5.96 |
| Distanza: | 446.429 parsec |
| Moto proprio RA: | -4.3 |
| Moto proprio Dec: | 44 |
| B-T magnitude: | 6.237 |
| V-T magnitude: | 6.025 |
Cataloghi e designazioni:
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INHABITED SKY
