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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.
| VLT UVES Observations of Interstellar Molecules and Diffuse Bands in the Magellanic Clouds
We discuss the abundances of interstellar CH, CH+, and CN inthe Magellanic Clouds, derived from spectra of seven SMC and 13 LMCstars obtained (mostly) with the VLT UVES. CH and/or CH+ havenow been detected toward three SMC and nine LMC stars; CN is detectedtoward Sk 143 (SMC) and Sk -67 2 (LMC). These data represent nearly allthe optical detections of these molecular species in interstellar mediabeyond the Milky Way. In the LMC, the CH/H2 ratio iscomparable to that found for diffuse Galactic molecular clouds in foursight lines but is lower by factors of 2.5-4.0 in two others. In theSMC, the CH/H2 ratio is comparable to the local Galacticvalue in one sight line but is lower by factors of 10-15 in two others.The abundance of CH in the Magellanic Clouds thus appears to depend onlocal physical conditions and not just on metallicity. In both the SMCand the LMC, the observed relationships between the column density of CHand those of CN, CH+, Na I, and K I are generally consistentwith the trends observed in our Galaxy.Using existing data for the rotational populations of H2 inthese sight lines, we estimate temperatures, radiation field strengths,and local hydrogen densities for the diffuse molecular gas. The inferredtemperatures range from about 45 to 90 K, the radiation fields rangefrom about 1 to 900 times the typical local Galactic field, and thedensities (in most cases) lie between 100 and 600 cm-3.Densities estimated from the observed N(CH), under the assumption thatCH is produced via steady state gas-phase reactions, are considerablyhigher than those derived from H2. Much better agreement isfound by assuming that the CH is made via the (still undetermined)process(es) responsible for the observed CH+. A significantfraction of the CH and CH+ in diffuse molecular material inthe SMC and LMC may be produced in photon-dominated regions. Theexcitation temperature obtained from the populations of the two lowestCN rotational levels toward Sk -67 2 is quite consistent with thetemperature of the cosmic microwave background radiation measured withCOBE.Toward most of our targets, the UVES spectra also reveal absorption atvelocities corresponding to the Magellanic Clouds ISM from several ofthe strongest of the diffuse interstellar bands (DIBs; at 5780, 5797,and 6284 Å). On average, the three DIBs are weaker by factors of7-9 (LMC) and about 20 (SMC), compared to those typically observed inGalactic sight lines with similar N(H I), presumably due to the lowermetallicities and stronger radiation fields in the LMC and SMC. Thethree DIBs are also weaker (on average, but with some exceptions), byfactors of order 2-6, relative to E(B-V), N(Na I), and N(K I) in theMagellanic Clouds. The detection of several of the so-calledC2 DIBs toward Sk 143 and Sk -67 2 with strengths similar tothose in comparable Galactic sight lines, however, indicates that nosingle, uniform scaling factor (e.g., one related to metallicity)applies to all DIBs (or for all sight lines) in the Magellanic Clouds.Based on observations collected at the European Southern Observatory,Chile, under programs 67.C-0281, 70.D-0164, 72.C-0064, 72.C-0682, and74.D-0109.
| Multiple Outflows and Protostars near IC 348 and the Flying Ghost Nebula
Using optical (Hα, [S II], and i'), near-IR (H2, J, H,and KS), mid-IR (Spitzer Space Telescope IRAC 4.5 μm), andsubmillimeter (850 and 450 μm) data, we have examined the regionsurrounding the IC 348 cluster and the neighboring ``Flying GhostNebula'' (FGN) and found a multitude of shocks from protostellaroutflows including HH 211, which had previously not been detected invisible wavelength images. We have identified 13 protostars in theregion that drive protostellar outflows. The region surrounding the FGNis rich in ongoing star formation, with a number of outflows similar tothose found in other sites of moderate star formation in Perseus (e.g.,L1448, L1455, and Barnard 1). We have also found a candidate bent jet inthis region. The axis defined by the bending angle suggests that thissource may have been ejected from a multiple star system near the IC 348IR source.
| Spitzer Observations of IC 348: The Disk Population at 2-3 Million Years
We present near- and mid-infrared photometry obtained with the SpitzerSpace Telescope of ~300 known members of the IC 348 cluster. We mergethis photometry with existing ground-based optical and near-infraredphotometry in order to construct optical-infrared spectral energydistributions (SEDs) for all the cluster members and present a completeatlas of these SEDs. We employ these observations to investigate boththe frequency and nature of the circumstellar disk population in thecluster. The Spitzer observations span a wavelength range between 3.6and 24 μm, corresponding to disk radii of ~0.1-5 AU from the centralstar. The observations are sufficiently sensitive to enable the firstdetailed measurement of the disk frequency for very low mass stars atthe peak of the stellar initial mass function. Using measurements ofinfrared excess between 3.6 and 8.0 μm, we find the total frequencyof disk-bearing stars in the cluster to be 50%+/-6%. However, only30%+/-4% of the member stars are surrounded by optically thick,primordial disks, while the remaining disk-bearing stars are surroundedby what appear to be optically thin, anemic disks. Both these values arebelow previous estimates for this cluster. The disk fraction appears tobe a function of spectral type and stellar mass. The fraction of starswith optically thick disks ranges from 11%+/-8% for stars earlier thanK6 to 47%+/-12% for K6-M2 stars to 28%+/-5% for M2-M6 stars. The disklongevity and thus conditions for planet formation appear to be mostfavorable for the K6-M2 stars, which are objects of comparable mass tothe Sun for the age of this cluster. The optically thick disks aroundlater type (>M4) stars appear to be less flared than the disks aroundearlier type stars. This may indicate a greater degree of dust settlingand a more advanced evolutionary state for the late M disk population.Finally, we find that the presence of an optically thick dust disk iscorrelated with gaseous accretion, as measured by the strength ofHα emission. A large fraction of stars classified as classical TTauri stars possess robust, optically thick disks, and very few suchstars are found to be diskless. The majority (64%) of stars classifiedas weak-lined T Tauri stars are found to be diskless. However, asignificant fraction (12%) of these stars are found to be surrounded bythick, primordial disks. These results suggest that it is more likelyfor dust disks to persist in the absence of active gaseous accretionthan for active accretion to persist in the absence of dusty disks.
| A high-resolution spectroscopy survey of β Cephei pulsations in bright stars
We present a study of absorption line-profile variations in early-B typenear-main-sequence stars without emission lines. We have surveyed atotal of 171 bright stars using the Nordic Optical Telescope (NOTSA),William Herschel Telescope (ING) and Coudé Auxiliary Telescope(ESO). Our sample contains 75% of all O9.5-B2.5 III-V non-emission-linestars brighter than 5.5 mag. We obtained high signal-to-noise,high-resolution spectra of the SiIII λ4560 triplet - for 125stars of our sample we obtained more than one spectrum - and examinedthese for pulsational-like line-profile variations and/or structure. Weconclude that about half of our sample stars show evidence forline-profile variations (LPV). We find evidence for LPV in about 65% ofour sample stars brighter than V=5.5. For stars with rotationalbroadening V sin i 100 km s-1, we find evidence for LPVin about 75% of the cases. We argue that it is likely that these LPV areof pulsational origin, and that hence more than half of thesolar-neighbourhood O9.5-B2.5 III-V stars is pulsating in modes that canbe detected with high-resolution spectroscopy. We detected LPV in 64stars previously unknown to be pulsators, and label these stars as newβ Cep candidates. We conclude that there is no obvious differencein incidence of (pulsational) LPV for early-B type near-main-sequencestars in binaries or in OB associations, with respect to single fieldstars.
| Neutral carbon and CO emission in the core and the halo of dark cloud Barnard 5
Aims.The physical conditions and chemical structure in the dark cloud ofBarnard 5 and its surrounding atomic halo is studied.The impact of the halo on the line emission emerging from the molecularcloud is investigated.Methods.We present observations of the [CI]^3P1→ ^3P0 transition of neutral carbon and the low-J transitionsof 12CO and 13CO. The CO maps extend from the core(Av 7) to the northern cloud edge and into the halo(Av 1). They are complemented by deeply integrated [CI]spectra made along a 1D cut of similar extent. Escape probability andphoton-dominated region (PDR) models are employed to interpret theobservations.Results.12CO and 13CO are detected inthe cloud and the halo, while [CI] is detected only toward the molecularcloud. This occurs even though the neutral carbon column density is5 times larger than the CO column density in the halo, but it canbe understood in terms of excitation. The [CI] excitation is governed bycollisions even at the low halo densities, while the CO excitation isdominated by the absorption of line photons emitted by the nearbymolecular cloud. The upper limit on the neutral carbon column density inthe halo is 6× 1015 cm-2. The PDR studiesshow that even small column densities of H2 and CO, such as those in theB5 halo, can significantly change the [CI] and COline emission (pre-shielding). Since this effect decreases the [CI]intensity and increases the CO intensity, the largest impact is notedfor the [CI]/CO line ratios. For the B5 cloud, a PDRmodel with a molecular hydrogen column density of ~6×1019 cm-2 in the halo matches the observed [CI]/COline ratios best. Models with no pre-shielding, in contrast, suggesthigh gas densities that are in conflict with independently deriveddensities. The PDR models with a χ<1 demonstrate that the [CI]/COratios cannot be attributed solely to a reduced FUV field.
| A search for fine structure inside high resolution profiles of weak diffuse interstellar bands
This paper presents a survey of the high-resolution profiles ofselected, moderately weak diffuse interstellar bands (DIBs) between 4725and 6730 Å. In very high signal-to-noise spectra, obtained as aresult of averaging several individual exposures of reddened, early-typestars that show Doppler splitting of <2 km s-1 ininterstellar gas lines, the profiles seem to have a substructure. Thissupports the molecular origin hypothesis for DIBs. We studied theprofiles of the diffuse interstellar bands at wavelengths of 4726.33,4963.85, 5418.89, 5541.74, 5544.95, 5546.46, 5762.73, 5766.05, 5769.09,6439.41, 6445.53, 6449.16, 6729.28 Å.
| Evolution of interacting binaries with a B type primary at birth
We revisited the analytical expression for the mass ratio distributionfor non-evolved binaries with a B type primary. Selection effectsgoverning the observations were taken into account in order to comparetheory with observations. Theory was optimized so as to fit best withthe observed q-distribution of SB1s and SB2s. The accuracy of thistheoretical mass ratio distribution function is severely hindered by theuncertainties on the observations. We present a library of evolutionarycomputations for binaries with a B type primary at birth. Some liberalcomputations including loss of mass and angular momentum during binaryevolution are added to an extensive grid of conservative calculations.Our computations are compared statistically to the observeddistributions of orbital periods and mass ratios of Algols. ConservativeRoche Lobe Over Flow (RLOF) reproduces the observed distribution oforbital periods but fails to explain the observed mass ratios in therange q in [0.4-1]. In order to obtain a better fit the binaries have tolose a significant amount of matter, without losing much angularmomentum.
| 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.
| 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.
| B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?
Projected rotational velocities (vsini) have been measured for 216 B0-B9stars in the rich, dense h and χ Persei double cluster and comparedwith the distribution of rotational velocities for a sample of fieldstars having comparable ages (t~12-15 Myr) and masses (M~4-15Msolar). For stars that are relatively little evolved fromtheir initial locations on the zero-age main sequence (ZAMS) (those withmasses M~4-5 Msolar), the mean vsini measured for the h andχ Per sample is slightly more than 2 times larger than the meandetermined for field stars of comparable mass, and the cluster and fieldvsini distributions differ with a high degree of significance. Forsomewhat more evolved stars with masses in the range 5-9Msolar, the mean vsini in h and χ Per is 1.5 times thatof the field; the vsini distributions differ as well, but with a lowerdegree of statistical significance. For stars that have evolvedsignificantly from the ZAMS and are approaching the hydrogen exhaustionphase (those with masses in the range 9-15 Msolar), thecluster and field star means and distributions are only slightlydifferent. We argue that both the higher rotation rates and the patternof rotation speeds as a function of mass that differentiatemain-sequence B stars in h and χ Per from their field analogs werelikely imprinted during the star formation process rather than a resultof angular momentum evolution over the 12-15 Myr cluster lifetime. Wespeculate that these differences may reflect the effects of the higheraccretion rates that theory suggests are characteristic of regions thatgive birth to dense clusters, namely, (1) higher initial rotationspeeds; (2) higher initial radii along the stellar birth line, resultingin greater spin-up between the birth line and the ZAMS; and (3) a morepronounced maximum in the birth line radius-mass relationship thatresults in differentially greater spin-up for stars that become mid- tolate-B stars on the ZAMS.
| Deuterated molecular hydrogen in the Galactic ISM. New observations along seven translucent sightlines
We present column density measurements of the HD molecule in theinterstellar gas toward 17 Galactic stars. The values for the seven mostheavily reddened sightlines, with E(B-V) = 0.38-0.72, are derived fromobservations with the Far Ultraviolet Spectroscopic Explorer (FUSE). Theother ten values are from a reanalysis of spectra obtained withCopernicus. In all cases, high-resolution ground-based observations of KI and/or the CH molecule were used to constrain the gas velocitystructure and to correct for saturation effects. Comparisons of thecolumn densities HD, CH, CN, and K I in these 17 sightlines indicatethat HD is most tightly correlated with CH. Stringent lower limits tothe interstellar D/H ratio, derived from the HD/2H2 ratio,range from 3.7 × 10-7 to 4.3 × 10-6.Our results also suggest that the HD/H2 ratio increases withthe molecular fraction f(H2) and that the interstellar D/Hratio might be obtained from HD by probing clouds with f(H2) 1. Finally, we note an apparent relationship between the molecularfractions of hydrogen and deuterium.
| Correlations between diffuse interstellar bands and atomic lines
We present and discuss correlations between strengths of the well-known,strong interstellar atomic lines of KI and CaII, and four selected,strong unidentified diffuse interstellar bands (DIBs): 5780, 5797, 5850and 6614. In order to analyse a homogeneous sample of echellehigh-resolution spectra it has been chosen to use measurements fromTerskol Observatory in Northern Caucasus plus a selected number ofhigher resolution observations performed using other instruments. Wedemonstrate that the strength of certain DIBs correlate well withneutral potassium lines and to a much lower degree with ionized calciumlines. This fact suggests that the degree of irradiation of a cloud withUV photons, capable to ionize interstellar atoms, plays a crucial rolein the formation/maintenance of certain molecular species: possiblecarriers of DIBs.
| The Interstellar Rubidium Isotope Ratio toward ρ Ophiuchi A
The isotope ratio 85Rb/87Rb places constraints onmodels of the nucleosynthesis of heavy elements, but there is no precisedetermination of the ratio for material beyond the solar system. Wereport the first measurement of the interstellar Rb isotope ratio. Ourmeasurement of the Rb I line at 7800 Å for the diffuse gas towardρ Oph A yields a value of 1.21+/-0.30 (1 σ) that differssignificantly from the meteoritic value of 2.59. The Rb/K elementalabundance ratio for the cloud also is lower than that seen inmeteorites. Comparison of the 85Rb/K and 87Rb/Kratios with meteoritic values indicates that the interstellar85Rb abundance in this direction is lower than the solarsystem abundance. We attribute the lower abundance to a reducedcontribution from the r-process. Interstellar abundances for Kr, Cd, andSn are consistent with much less r-process synthesis for the solarneighborhood compared to the amount inferred for the solar system.
| XMM-Newton study of the very young stellar cluster IC 348
We analyze a XMM-Newton X-ray imaging observation of the very youngstellar cluster IC 348 with an observing time of 12 h and acorresponding total (all detector) MOS-equivalent exposure time of 207ks. Our observation is strongly affected by a very intense solarparticle flare, due to which only the first half of the exposure timecan be used for scientific analysis. We compare the X-ray sources seenby XMM-Newton with those found in our previous Chandra study of IC 348and find that XMM-Newton reveals 71 new X-ray sources, most of which arelocated outside the field-of-view of the Chandra observation. 20 ofthese new X-ray sources can be identified with known cluster members,and 19 sources are likely to be new low-mass members of the cluster. Thelightcurves of the XMM-Newton sources show at most moderate levels ofvariability, but no large flares. We compare the spectral fittingresults for 10 stars for which we have good spectra from both Chandraand XMM-Newton, and find good agreement in the fitted plasmatemperatures, but a systematic difference in the fitted values of thehydrogen column density (extinction). We finally discuss the X-rayproperties of the optically bright B1 star o Per and the X-raydetections among the deeply embedded young stellar objects to the southof the optical cluster center (including HH 211-mm), and find that noneof the 23 spectroscopically identified brown dwarfs in IC 348 isdetected in our XMM-Newton data.
| On the relation between diffuse bands and column densities of H2, CH and CO molecules
Mutual relations between column densities of H2, CH and COmolecules as well as between the latter and strengths of the major 5780and 5797 diffuse bands are presented and discussed. The CH radical seemsto be a good H2 tracer, possibly better than CO. It is alsodemonstrated that the molecular fraction of the H2 moleculeis correlated with an intensity ratio of 5797 and 5780 DIBs, suggestingthe possible formation of narrow DIB carriers in denser clouds,dominated by molecular hydrogen and reasonably shielded from ionizing UVradiation by small dust grains.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/949
| On the Origin of the Dispersion in the 7Li/6Li Ratio in the ISM
Measurements of the 7Li/6Li ratio in the localinterstellar medium (ISM) towards o Per and ζ Per by Knauth et al.(2000, AAA 073.131.129) show clouds with a range from near 2 (a valuewhich points to GCR production by spallation or alpha + alpha to near 11(the solar system value). These values can be very well accounted forwithin our model of general chemical enrichment of the Galaxy in which akey role is played by the continuing infall of metal-poor extragalacticgas to the Galactic plane, in the form of high-velocity clouds. Withinthis model, light nuclides are produced in the ISM, but destroyed indense hot interstellar regions around massive stars, the process ofwhich yields a differential depletion of 6Li relative to7Li, which can vary on quite short-distance scales.
| 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.
| 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.
| An Ultra-high-Resolution Survey of the Interstellar 7Li/6Li Isotope Ratio in the Solar Neighborhood
In an effort to probe the extent of variations in the interstellar7Li/6Li ratio seen previously,ultra-high-resolution (R~360,000), high signal-to-noise spectra of starsin the Perseus OB2 and Scorpius OB2 associations were obtained. Thesemeasurements confirm our earlier findings of an interstellar7Li/6Li ratio of about 2 toward ο Per, thevalue predicted from models of Galactic cosmic-ray spallation reactions.Observations of other nearby stars yield limits consistent with theisotopic ratio of ~12 seen in carbonaceous chondrite meteorites. If thisratio originally represented the gas toward ο Per, then todecrease the original isotope ratio to its current value an order ofmagnitude increase in the Li abundance is expected, but it is not seen.The elemental K/Li ratio is not unusual, although Li and K are formedvia different nucleosynthetic pathways. Several proposals to account forthe low 7Li/6Li ratio were considered, but noneseems satisfactory. Analysis of the Li and K abundances from our surveyhighlighted two sight lines where depletion effects are prevalent. Thereis evidence for enhanced depletion toward X Per, since both abundancesare lower by a factor of 4 when compared to other sight lines. Moreover,a smaller Li/H abundance is observed toward 20 Aql, but the K/Habundance is normal, suggesting enhanced Li depletion (relative to K) inthis direction. Our results suggest that the7Li/6Li ratio has not changed significantly duringthe last 4.5 billion years and that a ratio of ~12 represents most gasin the solar neighborhood. In addition, there appears to be a constantstellar contribution of 7Li, indicating that one or twoprocesses dominate its production in the Galaxy.
| 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.
| Apsidal Motion in Binaries: Rotation of the Components
A sample of 51 separated binary systems with measured apsidal periodsand rotational velocities of the components is examined. The ranges ofthe angles of inclination of the equatorial planes of the components tothe orbital plane are estimated for these systems. The observed apsidalvelocities can be explained by assuming that the axes of rotation of thestars are nonorthogonal to the orbital plane in roughly 47% of thesystems (24 of the 51) and the rotation of the components is notsynchronized with the orbital motion in roughly 59% of the systems (30of 51). Nonorthogonality and nonsynchrony are defined as deviations from90° and a synchronized angular velocity, respectively, at levels of1 or more.
| 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.
| 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.
| A Study of the Luminosity and Mass Functions of the Young IC 348 Cluster Using FLAMINGOS Wide-Field Near-Infrared Images
We present wide-field near-infrared (JHK) images of the young, τ=2Myr IC 348 cluster taken with FLAMINGOS. We use these new data toconstruct an infrared census of sources, which is sensitive enough todetect a 10 MJup brown dwarf seen through an extinctionof AV~7. We examine the cluster's structure and relationshipto the molecular cloud and to construct the cluster's K-band luminosityfunction. Using our model luminosity function algorithm, we derive thecluster's initial mass function (IMF) throughout the stellar andsubstellar regimes and find that the IC 348 IMF is very similar to thatfound for the Trapezium cluster, with both cluster IMFs having a modebetween 0.2-0.08 Msolar. In particular, we find that,similar to our results for the Trapezium, brown dwarfs constitute onlyone in four of the sources in the IC 348 cluster. We show that a modestsecondary peak forms in the substellar IC 348 K-band luminosity function(KLF), corresponding to the same mass range responsible for a similarKLF peak found in the Trapezium. We interpret this KLF peak as eitherevidence for a corresponding secondary IMF peak at the deuterium burninglimit or as arising from a feature in the substellar mass-luminosityrelation that is not predicted by current theoretical models. Finally,we find that IC 348 displays radial variations of its subsolar (0.5-0.08Msolar) IMF on a parsec scale. Whatever mechanism thatis breaking the universality of the IMF on small spatial scales in IC348 does not appear to be acting on the brown dwarf population, whoserelative size does not vary with distance from the cluster center.
| Radial velocities of early-type stars in the Perseus OB2 association
We present radial velocities for 29 B- and A-type stars in the field ofthe nearby association Perseus OB2. The velocities are derived fromspectra obtained with AURELIE, via cross correlation with radialvelocity standards matched as closely as possible in spectral type. Theresulting accuracy is ~ 2-3 km s-1. We use thesemeasurements, together with published values for a few other early-typestars, to study membership of the association. The mean radial velocity(and measured velocity dispersion) of Per OB2 is 23.5 +/- 3.9 kms-1, and lies ~ 15 km s-1 away from the meanvelocity of the local disk field stars. We identify a number ofinterlopers in the list of possible late-B- and A-type members which wasbased on Hipparcos parallaxes and proper motions, and discuss thecolour-magnitude diagram of the association.Based on observations made at the Observatoire de Haute-Provence (CNRS),France.
| Gas-phase recombination, grain neutralization and cosmic-ray ionization in diffuse gas
Atomic ions are mostly neutralized by small grains (or PAH molecules) incurrent theories of heating and cooling in cool diffuse clouds; in themain they do not recombine with free electrons. This alters theionization balance by depressing n(H+) and n(He+)while carbon generally remains nearly fully once-ionized: chargeexchange with atomic oxygen and formation of H2 and OH alsodepress n(H+) in partly molecular gas. Seemingly restrictiveempirical limits on {zetaH are relaxed and higher values forzetaH are favored in a wide range of circumstances, whengrain neutralization is recognized. Maintenance of the proton density atlevels needed to reproduce observations of HD requires zeta,SUB>H>~ 2x 10-16 s-1, but such models naturallyexplain the presence of both HD and H3+ inrelatively tenuous H I clouds. In dense gas, a higher ionization ratecan account for high observed fractions of atomic hydrogen, andrecognition of the effects of grain neutralization can resolve a majorparadox in the formation of sulfur-bearing compounds.
| Interferometric Observations of the H II Region Around xi Per
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| A Far Ultraviolet Spectroscopic Explorer Survey of Interstellar Molecular Hydrogen in Translucent Clouds
We report the first ensemble results from the Far UltravioletSpectroscopic Explorer survey of molecular hydrogen in lines of sightwith AV>~1 mag. We have developed techniques for fittingcomputed profiles to the low-J lines of H2, and thusdetermining column densities for J=0 and J=1, which contain >~99% ofthe total H2. From these column densities and ancillary datawe have derived the total H2 column densities, hydrogenmolecular fractions, and kinetic temperatures for 23 lines of sight.This is the first significant sample of molecular hydrogen columndensities of ~1021 cm-2, measured through UVabsorption bands. We have also compiled a set of extinction data forthese lines of sight, which sample a wide range of environments. We havesearched for correlations of our H2-related quantities withpreviously published column densities of other molecules and extinctionparameters. We find strong correlations between H2 andmolecules such as CH, CN, and CO, in general agreement with predictionsof chemical models. We also find the expected correlations betweenhydrogen molecular fraction and various density indicators such askinetic temperature, CN abundance, the steepness of the far-UVextinction rise, and the width of the 2175 Å bump. Despite therelatively large molecular fractions, we do not see the values greaterthan 0.8 expected in translucent clouds. With the exception of a fewlines of sight, we see little evidence for the presence of individualtranslucent clouds in our sample. We conclude that most of the lines ofsight are actually composed of two or more diffuse clouds similar tothose found toward targets like ζ Oph. We suggest a modification interminology to distinguish between a ``translucent line of sight'' and a``translucent cloud.''
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Observation and Astrometry data
| Constellation: | Persée |
| Right ascension: | 03h44m19.10s |
| Declination: | +32°17'18.0" |
| Apparent magnitude: | 3.83 |
| Distance: | 452.489 parsecs |
| Proper motion RA: | 9.3 |
| Proper motion Dec: | -13.7 |
| B-T magnitude: | 3.912 |
| V-T magnitude: | 3.906 |
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