내용
사진
사진 업로드
DSS Images Other Images
관련 글
A Compilation of Interstellar Column Densities
We have collated absorption line data toward 3008 stars in order tocreate a unified database of interstellar column densities. These datahave been taken from a number of different published sources and includemany different species and ionizations. The preliminary results from ouranalysis show a tight relation [N(H)/E(B - V) = 6.12 ×1021] between N(H) and E(B - V). Similar plots havebeen obtained with many different species, and their correlations alongwith the correlation coefficients are presented.
| Very Large Telescope/X-shooter Spectroscopy of the Candidate Black Hole X-Ray Binary MAXI J1659-152 in Outburst
We present the optical to near-infrared spectrum of MAXI J1659-152during the onset of its 2010 X-ray outburst. The spectrum was obtainedwith X-shooter on the ESO Very Large Telescope early in the outburstsimultaneous with high-quality observations at both shorter and longerwavelengths. At the time of the observations, the source was in thelow-hard state. The X-shooter spectrum includes many broad (~2000 kms-1), double-peaked emission profiles of H, He I, and He II,characteristic signatures of a low-mass X-ray binary during outburst. Wedetect no spectral signatures of the low-mass companion star. Thestrength of the diffuse interstellar bands results in a lower limit tothe total interstellar extinction of AV ~= 0.4 mag. Using theneutral hydrogen column density obtained from the X-ray spectrum weestimate AV ~= 1 mag. The radial velocity structure of theinterstellar Na I D and Ca II H&K lines results in a lower limit tothe distance of ~4 ± 1 kpc, consistent with previous estimates.With this distance and AV , the dereddened spectral energydistribution represents a flat disk spectrum. The two 10 minuteX-shooter spectra show significant variability in the red wing of theemission-line profiles, indicating a global change in the densitystructure of the disk, though on a timescale much shorter than thetypical viscous timescale of the disk.Based on ESO-VLT/X-shooter observations obtained using the X-shooterguaranteed time GRB program (086.A-0073).
| E-BOSS: an Extensive stellar BOw Shock Survey. I. Methods and first catalogue
Context. Bow shocks are produced by many astrophysical objects whereshock waves are present. Stellar bow shocks, generated by runaway stars,have been previously detected in small numbers and well-studied. Alongwith progress in model development and improvements in observinginstruments, our knowledge of the emission produced by these objects andits origin can now be more clearly understood. Aims: We produce astellar bow-shock catalogue by applying uniform search criteria and asystematic search process. This catalogue is a starting point forstatistical studies, to help us address fundamental questions such as,for instance, the conditions under wich a stellar bow shock isdetectable. Methods: By using the newest infrared data releases,we carried out a search for bow shocks produced by early-type runawaystars. We first explored whether a set of known IRAS bow shockcandidates are visible in the most recently available IR data, which hasmuch higher resolution and sensitivity. We then carried out a selectionof runaway stars from the latest, large runaway catalogue available. Inthis first release, we focused on OB stars and searched for bow-shapedfeatures in the vicinity of these stars. Results: We provide abow-shock candidate survey that gathers a total of 28 members, which wecall the Extensive stellar BOw Shock Survey (E-BOSS). We derive the mainbow-shock parameters, and present some preliminary statistical resultson the detected objects. Conclusions: Our analysis of the initialsample and the newly detected objects yields a bow-shock detectabilityaround OB stars of ~10 per cent. The detections do not seem to dependparticularly on either stellar mass, age or position. The extension ofthe E-BOSS sample, with upcoming IR data, and by considering, forexample, other spectral types as well, will allow us to perform a moredetailed study of the findings.
| A Tale of Two Mysteries in Interstellar Astrophysics: The 2175 Å Extinction Bump and Diffuse Interstellar Bands
The diffuse interstellar bands (DIBs) are ubiquitous absorption spectralfeatures arising from the tenuous material in the space betweenstars—the interstellar medium (ISM). Since their first detectionnearly nine decades ago, over 400 DIBs have been observed in the visibleand near-infrared wavelength range in both the Milky Way and externalgalaxies, both nearby and distant. However, the identity of the speciesresponsible for these bands remains as one of the most enigmaticmysteries in astrophysics. An equally mysterious interstellar spectralsignature is the 2175 Å extinction bump, the strongest absorptionfeature observed in the ISM. Its carrier also remains unclear since itsfirst detection 46 years ago. Polycyclic aromatic hydrocarbon (PAH)molecules have long been proposed as a candidate for DIBs as theirelectronic transitions occur in the wavelength range where DIBs areoften found. In recent years, the 2175 Å extinction bump is alsooften attributed to the ?-?* transition in PAHs. If PAHs areindeed responsible for both the 2175 Å extinction feature andDIBs, their strengths may correlate. We perform an extensive literaturesearch for lines of sight for which both the 2175 Å extinctionfeature and DIBs have been measured. Unfortunately, we found nocorrelation between the strength of the 2175 Å feature and theequivalent widths of the strongest DIBs. A possible explanation might bethat DIBs are produced by small free gas-phase PAH molecules and ions,while the 2175 Å bump is mainly from large PAHs or PAH clusters incondensed phase so that there is no tight correlation between DIBs andthe 2175 Å bump.
| Searching for Naphthalene Cation Absorption in the Interstellar Medium
Interstellar naphthalene cations (C10H+8) have been proposed by a study to be the carriers of asmall number of diffuse interstellar bands (DIBs). Using an archive ofhigh signal-to-noise spectra obtained at the Apache Point Observatory,we used two methods to test the hypothesis. Both methods failed todetect significant absorption at lab wavelengths of interstellar spectrawith laboratory spectra. We thereby conclude thatC10H+ 8 is not a DIB carrier in typicalreddened sight lines.
| Dust properties along anomalous extinction sightlines. II. Studying extinction curves with dust models
Context. Studies of the dust extinction in the Galaxy have found thatthe large majority of sight lines analyzed obey a simple relationdepending on one parameter, the total-to-selective extinctioncoefficient, RV. Different values of RV are ableto match the whole extinction curve in different environments, thuscharacterize normal extinction curves. However anomalous curves i.e,curves which deviate strongly from this simple behavior have beenobserved in the Galaxy as well as external galaxies. Aims: Morethan sixty curves with large ultraviolet deviations from their best-fitone-parameter curve are analyzed. The extinction curves are fitted withdust models to shed light on the properties of the grains along selectedlines of sight, the processes affecting them, and their relations withthe environmental characteristics. Methods: The extinction curvemodels are developed using the latest prescriptions for grain-sizedistributions capable of describing one-parameter curves forRV values from 3.1 to 5.5. These models, extended here downto RV = 2.0, allow us to compare the resulting properties ofour deviating curves with those of normal curves in a self-consistentframework, and thus to recover the relative trends overcoming themodeling uncertainties. Results: In addition to 20 anomalouscurves extracted from the same sample for study in a previous paper andrevised here to account for the latest updates, these curves representthe largest, homogeneous sample of anomalous curves studied so far withdust models. Our results show that the ultraviolet deviations are drivenby a larger amount of small grains than predicted for lines of sightwhere extinction depends on only one parameter. Moreover, thedust-to-gas ratios of anomalous curves are lower than the same valuesfor no deviating lines of sight. Conclusions: Both shocks andgrain-grain collisions should destroy dust grains, hence reduce theamount of the dust trapped in the grains, modify the size distributionof the dust, and increase the small-to-large grain size ratio.Therefore, the extinction properties derived should correspond to sightlines where shocks and high velocity flows perturb the physical state ofthe interstellar medium and leave their signature on the dustproperties.
| Polycyclic Aromatic Hydrocarbons and the Diffuse Interstellar Bands: A Survey
We discuss the proposal of relating the origin of some of the diffuseinterstellar absorption bands (DIBs) to neutral polycyclic aromatichydrocarbons (PAHs) present in translucent interstellar clouds. Anassessment of ionized PAHs will be examined in a future report. Thespectra of several cold, isolated gas-phase PAHs have been measured inthe laboratory under experimental conditions that mimic the interstellarconditions and are compared with an extensive set of astronomicalspectra of reddened, early-type stars. This comparisonprovides—for the first time—accurate upper limits for theabundances of specific PAH molecules along specific lines of sight,something not attainable from IR observations alone. The comparison ofthese unique laboratory data with high-resolution, high signal-to-noiseratio spectra leads to two major findings: (1) a finding specific to theindividual molecules that were probed in this study and, which leads tothe clear and unambiguous conclusion that the abundance of thesespecific neutral PAHs must be very low in the individual translucentinterstellar clouds that were probed in this survey (PAH features remainbelow the level of detection) and, (2) a general finding that neutralPAHs exhibit intrinsic band profiles that are similar to the profile ofthe narrow DIBs indicating that the carriers of the narrow DIBs musthave close molecular structure and characteristics. This study is thefirst quantitative survey of neutral PAHs in the optical range and itopens the way for unambiguous quantitative searches of PAHs in a varietyof interstellar and circumstellar environments.
| Studies of Diffuse Interstellar Bands V. Pairwise Correlations of Eight Strong DIBs and Neutral Hydrogen, Molecular Hydrogen, and Color Excess
We establish correlations between equivalent widths of eight diffuseinterstellar bands (DIBs), and examine their correlations with atomichydrogen, molecular hydrogen, and E B-V . The DIBs arecentered at ?? 5780.5, 6204.5, 6283.8, 6196.0, 6613.6,5705.1, 5797.1, and 5487.7, in decreasing order of Pearson's correlationcoefficient with N(H) (here defined as the column density of neutralhydrogen), ranging from 0.96 to 0.82. We find the equivalent width (EW)of ?5780.5 is better correlated with column densities of H thanwith E B-V or H2, confirming earlier resultsbased on smaller data sets. We show that the same is true for six of theseven other DIBs presented here. Despite this similarity, the eightstrong DIBs chosen are not correlated well enough with each other tosuggest they come from the same carrier. We further conclude that theseeight DIBs are more likely to be associated with H than withH2, and hence are not preferentially located in the densest,most UV shielded parts of interstellar clouds. We suggest that theyarise from different molecules found in diffuse H regions with verylittle H2 (molecular fraction f < 0.01). Of the 133 starswith available data in our study, there are three with significantlyweaker ?5780.5 than our mean H-?5780.5 relationship, allof which are in regions of high radiation fields, as previously noted byHerbig. The correlations will be useful in deriving interstellarparameters when direct methods are not available. For instance, withcare, the value of N(H) can be derived from W?(5780.5).
| Doppler splitting in diffuse interstellar bands
We demonstrate evident Doppler splitting in the profiles of many narrowdiffuse interstellar bands (DIBs). Their components are compared withthose of atomic and molecular lines of interstellar origin. It is shownthat it is likely that the species that shares both wavelength shiftsand strength ratios of the Doppler components seen in the DIB profilesis the CH radical. Because of this profile resemblance, it isrecommended that CH lines can be used to shift spectra to the restvelocity frame for interstellar features, especially to determine theDIB rest wavelengths on the basis of the CH line at 4300.3132 Å inthe spectrum of HD147889. Our results strongly support a molecularorigin of diffuse bands.
| Studies of the Diffuse Interstellar Bands. IV. The Nearly Perfect Correlation Between ??6196.0 and 6613.6
In a sample of 114 diffuse cloud sightlines spanning a wide range ofinterstellar environments, we find the equivalent widths of the diffuseinterstellar bands (DIBs) ?6196.0 and ?6613.6 to beextremely well correlated, with a correlation coefficient of 0.986. Amaximum likelihood functional relationship analysis shows that theobservations are consistent with a perfect correlation if theobservational errors, which are dominated by continuum placement andother systematics such as interfering lines, have been underestimated bya factor of 2. The quality of this correlation far exceeds otherpreviously studied correlations, such as that between the ?5780.5DIB and either the color excess or the atomic hydrogen column density.The unusually tight correlation between these two DIBs would seem tosuggest that they might represent the first pair of DIBs known to be dueto the same molecular carrier. However, further theoretical work will berequired to determine whether the different linewidths and band shapesof these two DIBs can be consistent with a common carrier. If the twoDIBs do not in fact share the same molecular carrier, their two carriersmust be chemically very closely related.
| The New Detections of 7Li/6Li Isotopic Ratio in the Interstellar Media
We have determined the isotopic abundance ratio of7Li/6Li in the interstellar media (ISMs) alonglines of sight to HD169454 and HD250290 using the High-DispersionSpectrograph on the Subaru Telescope. We also observed ? Oph forcomparison with previous data. The observed abundance ratios were7Li/6Li = 8.1+3.6 -1.8 and6.3+3.0 -1.7 for HD169454 and HD250290,respectively. These values are in reasonable agreement with thoseobserved previously in the solar neighborhood ISMs within±2? error bars and are also consistent with our measurementof 7Li/6Li = 7.1+2.9 -1.6for a cloud along the line of sight to ? Oph. This is good evidencefor homogeneous mixing and instantaneous recycling of the gas componentin the Galactic disk. We also discuss several source compositions of7Li, Galactic cosmic-ray interactions, stellarnucleosynthesis, and big bang nucleosynthesis.Based on data collected at Subaru Telescope, which is operated by theNational Astronomical Observatory of Japan.
| A CO J = 1-0 survey of common optical/uv absorption sightlines
Context: Comparison of optical/uv absorption line data withhigh-resolution profiles of mm-wave CO emission provides complementaryinformation on the absorbing gas, as toward ? Oph. Over the pastthirty years a wealth of observations of CO and other molecules inoptical/uv absorption in diffuse clouds has accumulated for which nocomparable CO emission line data exist. Aims: To acquire mm-waveJ=1-0 CO emission line profiles toward a substantial sample ofcommonly-studied optical/uv absorption line targets and to compare withthe properties of the absorbing gas, especially the predicted emissionline strengths. Methods: Using the ARO 12 m telescope, weobserved mm-wavelength J=1-0 CO emission with spectral resolution R ?3× 106 and spatial resolution 1' toward a sample of 110lines of sight previously studied in optical/uv absorption lines of CO,H2, CH, etc. Results: Interstellar CO emission was detected along65 of the 110 lines of sight surveyed and there is a generalsuperabundance of CO emission given the distribution of galacticlatitudes in the survey sample. Much of the emission is optically thickor very intense and must emanate from dark clouds or warm dense gas nearHII regions. Conclusions: Judging from the statisticalsuperabundance of CO emission, seen also in the total line of sightreddening, the OB star optical/uv absorption line targets must bephysically associated with the large quantities of neutral gas whose COemission was detected, in which case they are probably influencing theabsorbing gas by heating and/or photoionizing it. This explains whyCO/H2 and 12CO/13CO ratios differ somewhat betweenuv and mm-wave absorption line studies. Because the lines of sight havebeen preselected to have AV ? 1 mag, relatively little ofthe associated material actually occults the targets, making itdifficult for CO emission line observations to isolate the foregroundgas contribution.Based on observations obtained with the ARO Kitt Peak 12 mtelescope.
| An Analysis of the Shapes of Interstellar Extinction Curves. V. The IR-through-UV Curve Morphology
We study the IR-through-UV interstellar extinction curves towards 328Galactic B and late-O stars. We use a new technique which employsstellar atmosphere models in lieu of unreddened "standard" stars. Thistechnique is capable of virtually eliminating spectral mismatch errorsin the curves. It also allows a quantitative assessment of the errorsand enables a rigorous testing of the significance of relationshipsbetween various curve parameters, regardless of whether theiruncertainties are correlated. Analysis of the curves gives the followingresults: (1) In accord with our previous findings, the central positionof the 2175 A extinction bump is mildly variable, its width is highlyvariable, and the two variations are unrelated. (2) Strong correlationsare found among some extinction properties within the UV region, andwithin the IR region. (3) With the exception of a few curves withextreme (i.e., large) values of R(V), the UV and IR portions of Galacticextinction curves are not correlated with each other. (4) The largesightline-to-sightline variation seen in our sample implies that anyaverage Galactic extinction curve will always reflect the biases of itsparent sample. (5) The use of an average curve to deredden a spectralenergy distribution (SED) will result in significant errors, and arealistic error budget for the dereddened SED must include the observedvariance of Galactic curves. While the observed largesightline-to-sightline variations, and the lack of correlation among thevarious features of the curves, make it difficult to meaningfullycharacterize average extinction properties, they demonstrate thatextinction curves respond sensitively to local conditions. Thus, eachcurve contains potentially unique information about the grains along itssightline.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Diffuse interstellar bands of unprecedented strength in the line of sight towards high-mass X-ray binary 4U 1907+09
High-resolution VLT/UVES spectra of the strongly reddened O supergiantcompanion to the X-ray pulsar 4U 1907+09 provide aunique opportunity to study the nature of the diffuse interstellar bands(DIBs) at unprecedented strength. We detect about 180 known DIBs, ofwhich about 25 were listed as tentative and are now confirmed. A dozennew DIB candidates longwards of 6900 Å are identified. We showthat the observed 5797 Å DIB strength is in line with the Galacticcorrelation with reddening, whereas the 5780 Å DIB strength isrelatively weak. This indicates the contribution of denser regions,where the UV penetration is reduced. The presence of dense cloud coresis supported by the detection of C2 rotational transitions. Members ofone DIB family (5797, 6379 Å and 6196, 6613 Å) behavecoherently, although one can make a distinction between the twocorrelated pairs. The broadened profiles of narrow DIBs are shown to beconsistent with the premise that each of the main clouds in the line ofsight discerned in the interstellar K I profile is contributingproportionally to the DIB profile. We complement and extend the relationof DIB strength with reddening {E}(B-V), as well as withneutral hydrogen column density N(H I), respectively, using stronglyreddened sightlines towards another four distant HMXBs. The 5780 ÅDIB, and tentatively also the 5797 and 6613 Å DIBs, are bettercorrelated to the gas tracer H I than to the dust tracer{E}(B-V). The resulting relationship can be applied to anyline of sight to obtain an estimate of the H I column density. In thesearch for the nature of the DIB carrier, this strongly reddened line ofsight is a complementary addition to single cloud line of sight studies.
| 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.
| 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.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| 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.
| A Critical Examination of the l-C3H-2 Spectrum and the Diffuse Interstellar Bands
It has recently been suggested by J. P. Maier's group that the originband and three vibronic bands of the linear propadienylidene anionl-C3H-2 match the diffuse interstellarbands (DIBs). We have examined the wavelength ranges in question usingdata from our ongoing DIB survey at the Apache Point Observatory. Wefind that the strongest DIB (λ6993) is not an acceptablewavelength match to the origin band ofl-C3H-2, based on high-resolutionlaboratory data. The nondetection of interstellar features correspondingto the K=2<--1 and K=0<--1 branches of paral-C3H-2 also argues against theassignment of λ6993 to the K=1<--0 branch of orthol-C3H-2. Two of the three DIBs thathave been attributed to vibronic bands do not correlate in intensitywith λ6993, providing further evidence against the assignment ofthis set of DIBs to l-C3H-2.
| Identification of the naphthalene cation in space?
A painstaking comparison of laboratory gas-phase spectra of thenaphthalene cation with an extensive set of astrophysical spectra wascarried out. In the vicinity of both naphthalene features, found in thelaboratory experiment, we detected relevant interstellar features. Thestrongest of them is situated at 6710.5Å, which is reasonablyclose to the laboratory feature at 6706.5Å and which is also ofcomparable width, i.e. about 20Å. The second feature was found at6493Å - also close to the 6488.4-Å laboratory band of asimilar width. The structures can be observed only in spectra of O starsbecause of the growing stellar line contamination in colder objects. Thepossible third feature is intertwined with a strong stellar helium line,but the unusual strength of the latter suggests that this naphthalenecation band is present as well as the two former ones. We estimated thecolumn density of the carrier, for the reddening value E(B-V)=1.0, asroughly 4×1015cm-2. The lack of precisewavelength coincidence between laboratory and observed features,however, makes the identification uncertain and further laboratory andobservational works are both highly desirable.
| Far-ultraviolet extinction and diffuse interstellar bands
We relate the equivalent widths of the major diffuse interstellar bands(DIBs) near 5797 and 5780Å with different colour excesses,normalized by E(B-V), which characterize the growth of interstellarextinction in different wavelength ranges. It is demonstrated that thetwo DIBs correlate best with different parts of the extinction curve,and the ratio of these diffuse bands is best correlated with thefar-ultraviolet (UV) rise. A number of peculiar lines of sight are alsofound, indicating that the carriers of some DIBs and the far-UVextinction can be separated in certain environments, e.g. towards thePer OB2 association.
| Absorption Wavelengths and Bandwidths for Interstellar Searches of C60 in the 2400-4100 Å Region
Low-temperature gas-phase wavelengths and bandwidths for astronomicalsearches for C60 in the 2400-4100 Å region aredetermined from the absorption spectra of C60 in rare gasmatrices at 4 K, coupled with information on the dependence of thevibronic transition frequencies of this fullerene on the Lorentz-Lorenzpolarizability parameter of matrices and solvents. These bandwidthsincrease from 25+/-5 cm-1 for the 11T1u-1 1Ag band at4024.0+/-0.5 Å to 2300+/-200 cm-1 for the 61T1u-1 1Ag band at 2488+/-8Å. Spectral observations of astrophysical objects considered to belikely sites of C60 have been examined in the context of thewavelengths and bandwidths of bands of the allowed transitions ofC60 which we recommend for searches of this species. Nocertain positive assignment of a C60 band has been made inthe 2400-4100 Å spectral region of these objects. The physicalorigin of the observed C60 absorption bandwidths is analyzedand discussed in an appendix.
| The Search for Interstellar C60
The optical region of a number of reddened O-type stars has beenexamined on Keck I HIRES spectrograms (R=45,000) for evidence ofinterstellar C60. No absorption features were detected nearthe laboratory C60 wavelengths 3857 and 3980 Å. Aninterstellar feature is present at 6220.8 Å, but it isunacceptably far from the laboratory gas-phase wavelength of 6217.5Å. It is probably just another of the weak diffuse interstellarbands (DIBs), which are numerous in that spectral region. The mostastronomically promising C60 feature was measured in thelaboratory at 3284 Å in liquid or solid matrices. Its gas-phasewavelength can be inferred either from matrix shifts of C60features at longer wavelengths or from high-temperature gas-phasemeasurements. On that evidence, the interstellar feature could fallanywhere between about 3244 and 3306 Å. Its width is uncertain buthere is taken to be about 1 Å . No interstellar absorption fittingthese specifications and as strong as 16 mÅ has been detected inthe stars observed, including Cyg OB2/8A of E(B-V)=1.60. It follows thatin that particular line of sight and for the assumed FWHM of 1 Å ,N(C60)<4.5×1011 cm-2. However,some recent laboratory spectroscopy suggests that its width may be verymuch larger, in which case this limit would be invalid. At this upperlimit, the corresponding number of carbon atoms contained in neutralC60 indicates that that molecule would be only a minorcontributor to the total amount of C in that direction, and would beless than 1% of the amount that may be tied up in the DIBs. StrongerC60 bands are known in the laboratory at approximately 2110and 2566 Å, but the upper limit on 3284 Å suggests that theywill not be easy to detect without high resolution, high signal-to-noiseratio (S/N) satellite spectroscopy and better laboratory gas-phasewavelengths. An estimate of the column density ofC+60, under the assumption that the 9577, 9632Å bands are indeed due to C+60 and that thelaboratory f-value is correct, indicates that theC+60/C60 abundance in that line ofsight is greater than 100.
| A deep echelle survey and new analysis of diffuse interstellar bands
We report a deep survey of diffuse interstellar bands (DIBs) between3906 Ä and 6812 Ä under consistent observing conditions towardthree very reddened and five unreddened stars. BD+63deg1964's line-of-sight was shown to present exceptional DIB enhancement innumber as well as in strength. The early spectral type of the star andthe use of spectra of an unreddened comparison star of the same spectraltype allowed to limit stellar line residuals. Using careful reductionand analysis methods we discovered 60 new DIBs which are confirmed inthe reddened targets HD 183143 and BD+40deg 4220. We detected25 possible DIBs which still await further confirmation, but we did notdetect or confirm 28 previously reported DIBs. The present survey with226 confirmed DIBs, measured in three targets allows a detailed andhomogeneous statistical analysis on the distribution of DIB widths andintensities. Based on observations at Observatoire Haute Provence withthe spectrograph ELODIE Figures 6 to 40 are only available in electronicform at http://www.edpsciences.org
| Organic Molecules in the Interstellar Medium, Comets, and Meteorites: A Voyage from Dark Clouds to the Early Earth
Our understanding of the evolution of organic molecules, and theirvoyage from molecular clouds to the early solar system and Earth, haschanged dramatically. Incorporating recent observational results fromthe ground and space, as well as laboratory simulation experiments andnew methods for theoretical modeling, this review recapitulates theinventory and distribution of organic molecules in differentenvironments. The evolution, survival, transport, and transformation oforganics is monitored, from molecular clouds and the diffuseinterstellar medium to their incorporation into solar system materialsuch as comets and meteorites. We constrain gas phase and grain surfaceformation pathways to organic molecules in dense interstellar clouds,using recent observations with the Infrared Space Observatory (ISO) andground-based radiotelescopes. The main spectroscopic evidence forcarbonaceous compounds in the diffuse interstellar medium is discussed(UV bump at 2200 Å, diffuse interstellar bands, extended redemission, and infrared absorption and emission bands). We criticallyreview the signatures and unsolved problemsrelated to the main organiccomponents suggested to be present in the diffuse gas, such aspolycyclic aromatic hydrocarbons (PAHs), fullerenes, diamonds, andcarbonaceous solids. We also briefly discuss the circumstellar formationof organics around late-typestars. In the solar system, space missionsto comet Halley and observations of the bright comets Hyakutake andHale-Bopp have recently allowed a reexamination of the organic chemistryof dust and volatiles in long-period comets. We review the advances inthis area and also discuss progress being made in elucidating thecomplex organic inventory of carbonaceous meteorites. The knowledge oforganic chemistry in molecular clouds, comets, and meteorites and theircommon link provides constraints for the processes that lead to theorigin, evolution, and distribution of life in the Galaxy.
| The composition and nature of the dust shell surrounding the binary AFGL 4106
We present infrared spectroscopy and imaging of AFGL 4106. The 2.4-5 mum ISO-SWS spectrum reveals the presence of a cool, luminous star(Teff ~ 3750 K) in addition to an almost equally luminous Fstar (Teff ~ 7250 K). The 5-195 mu m SWS and LWS spectra aredominated by strong emission from circumstellar dust. We find that thedust consists of amorphous silicates, with a minor but significantcontribution from crystalline silicates. The amorphous silicates consistof Fe-rich olivines. The presence of amorphous pyroxenes cannot beexcluded but if present they contain much less Fe than the amorphousolivines. Comparison with laboratory data shows that the pure Mg-endmembers of the crystalline olivine and pyroxene solid solution seriesare present. In addition, we find strong evidence for simple oxides (FeOand Al_2O_3) as well as crystalline H_2O ice. Several narrow emissionfeatures remain unidentified. Modelling of the dust emission using adust radiation transfer code shows that large grains (~ 1 mu m) must bepresent and that the abundance of the crystalline silicates is between 7and 15% of the total dust mass, depending on the assumed enstatite toforsterite ratio, which is estimated to be between 1 and 3. Theamorphous and crystalline dust components in the shell do not have thesame temperature, implying that the different dust species are notthermally coupled. We find a dust mass of ~ 3.9 * 10(-2) M_sun expelledover a period of ~ 4 * 10(3) years for a distance of 3.3 kpc. The F-starin the AFGL 4106 binary is likely a post-red-supergiant in transition toa blue supergiant or WR phase. Based on observations with ISO, an ESAproject with instruments funded by ESA Member States (especially the PIcountries: France, Germany, the Netherlands and the United Kingdom) andwith the participation of ISAS and NASA Based on observations collectedat the European Southern Observatory, La Silla, Chile
| On the relation between diffuse interstellar bands and simple molecular species
We present observations of the major diffuse interstellar bands (DIBs)at 5780 and 5797 Ä as well as literature data and our ownobservations of the violet lines of CH and CH(+) , in the lines of sighttoward some 70 stars representing various degrees of the interstellarreddening. The correlations are shown and discussed in the context ofindicators such as far-UV extinction parameters and neutral molecularabundances. The results show that the DIBs in question (lambda lambda5797 and 5780) both probably form in diffuse cloud interiors, in arelated regime where CH and H_2 form. The ratio of the two DIBscorrelates with CH abundance, confirming that the lambda 5797 carrier isfavoured in enhanced molecular gas regions over the lambda 5780 carrier.The ratio of the two DIBs correlates poorly with CH(+) abundance. Ourcompilation of observational data also suggests that the DIB ratio maybe equally useful as a cloud type indicator as is R_V, the ratio oftotal to selective extinction, and much more readily observed. Based onobservations obtained at the Russian Special Astrophysical Observatory(SAO), Terskol Observatory (TER), Canada France Hawaii Telescope (CFHT),European Southern Observatory (ESO), Observatoire de Haute-Provence(OHP)
| 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.
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
