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Spectroscopic analyses of six suspected chemically peculiar stars
The abundance pattern of six stars classified as suspected chemicallypeculiar in the General Catalogue of Ap and Am stars by Renson has beenderived to ascertain the real nature of these objects. Spectroscopicobservations in the range λλ4800-5600 Å have beencarried out at the stellar station of the INAF - Catania AstrophysicalObservatory.Among the studied stars, for only three of them we confirmed theirpeculiarity, HD155102 being a silicon star, HD159082 a mercury-manganesestar and HD162132 a moderate metallic A-type star.The other three objects have chemical abundances not so different fromthe standard values derived in the literature for A-type stars and,furthermore, they do not show light variability. Hence, we suggest thatthey could be ruled out from Renson's catalogue.
| Infrared detection of gas phase formaldehyde towards the high mass protostar W33A
We report the detection of numerous absorption lines of theν1 band of gaseous formaldehyde (H2CO) near 3.6 μmtowards the high-mass protostar W33A. This is the first infrareddetection of gaseous H2CO in an interstellar cloud. An upper limittoward RAFGL 7009S is also reported. The column density of H2CO detectedat 3.6 μm toward W33A is much higher than that measured in large beammillimeter wave observations toward the same source, suggesting that itis concentrated close to the infrared continuum source. The meantemperature of the H2CO, derived from LTE spectral modelling, is ~100 K,which is close to the values found for most other gas phase speciesobserved in absorption and is the expected temperature of the cloud atthe dust mantle sublimation interface, implying a large jump in theabundance of gaseous H2CO from the surrounding cold cloud to the warmgas. The ratio of gaseous and solid H2CO column densities is about 0.03for W33A and less than 0.02 for RAFGL 7009S. We discuss this detectionin the context of the two most likely mechanisms for H2CO formation:grain mantle evaporation, and gas phase reactions between speciesproduced by photodissociation of grain mantle evaporants.
| Atlas and Catalog of Dark Clouds Based on Digitized Sky Survey I
We present a quantitative atlas and catalog of dark clouds derived byusing the optical database ``Digitized Sky Survey I''. Applying atraditional star-count technique to 1043 plates contained in thedatabase, we produced an AV map covering the entire region inthe galactic latitude range |b| ≤ 40°. The map was drawn at twodifferent angular resolutions of 6' and 18', and is shown in detail in aseries of figures in this paper. Based on the AV map, weidentified 2448 dark clouds and 2841 clumps located inside them. Somephysical parameters, such as the position, extent, and opticalextinction, were measured for each of the clouds and clumps. We alsosearched for counterparts among already known dark clouds in theliterature. The catalog of dark clouds presented in this paper lists thecloud parameters as well as the counterparts.
| Variability of Stars in the Pulkovo Spectrophotometric Catalog
We present the results of a statistical study of brightness variabilityfor 693 stars of the Pulkovo spectrophotometric database in fivespectral bands in the range λλ 320 1080 nm. Significantbrightness variations were detected in at least one spectral bandagainst the background of the random noise for one-third of the starsnot earlier believed to be variable. A comparison of the distributionsof these variations in amplitude and spectral band for the normal andvariable stars shows that variability is inherent to most stars to someextent and is often wavelength dependent.
| Observed Orbital Eccentricities
For 391 spectroscopic and visual binaries with known orbital elementsand having B0-F0 IV or V primaries, we collected the derivedeccentricities. As has been found by others, those binaries with periodsof a few days have been circularized. However, those with periods up toabout 1000 or more days show reduced eccentricities that asymptoticallyapproach a mean value of 0.5 for the longest periods. For those binarieswith periods greater than 1000 days their distribution of eccentricitiesis flat from 0 to nearly 1, indicating that in the formation of binariesthere is no preferential eccentricity. The binaries with intermediateperiods (10-100 days) lack highly eccentric orbits.
| A new look at the position of the 1604 Supernova (V843 Ophiuchi)
The position of the supernova of 1604 (V843 Oph) is re-assessed, withrelevant discussion pertaining to the present-day remnant, 3C 358.
| A near-infrared stellar spectral library: I. H-band spectra.
This paper presents the H band near-infrared (NIR) spectral library of135 solar type stars covering spectral types O5-M3 and luminosityclasses I-V as per MK classification. The observations were carried outwith 1.2 meter Gurushikhar Infrared Telescope (GIRT), at Mt. Abu, Indiausing a NICMOS3 HgCdTe 256 x 256 NIR array based spectrometer. Thespectra have a moderate resolution of 1000 (about 16 A) at the H bandand have been continuum shape corrected to their respective effectivetemperatures. This library and the remaining ones in J and K bands oncereleased will serve as an important database for stellar populationsynthesis and other applications in conjunction with the newly formedlarge optical coude feed stellar spectral library of Valdes et al.(2004). The complete H-Band library is available online at: http://vo.iucaa.ernet.in/~voi/NIR_Header.html
| Tidal Effects in Binaries of Various Periods
We found in the published literature the rotational velocities for 162B0-B9.5, 152 A0-A5, and 86 A6-F0 stars, all of luminosity classes V orIV, that are in spectroscopic or visual binaries with known orbitalelements. The data show that stars in binaries with periods of less thanabout 4 days have synchronized rotational and orbital motions. Stars inbinaries with periods of more than about 500 days have the samerotational velocities as single stars. However, the primaries inbinaries with periods of between 4 and 500 days have substantiallysmaller rotational velocities than single stars, implying that they havelost one-third to two-thirds of their angular momentum, presumablybecause of tidal interactions. The angular momentum losses increase withdecreasing binary separations or periods and increase with increasingage or decreasing mass.
| A 3-5 μ m VLT spectroscopic survey of embedded young low mass stars I. Structure of the CO ice
Medium resolution (lambda /Delta lambda = 5000-10 000) VLT-ISAACM-band spectra are presented of 39 young stellar objects in nearbylow-mass star forming clouds showing the 4.67 μm stretching vibrationmode of solid CO. By taking advantage of the unprecedentedly largesample, high S/N ratio and high spectral resolution, similarities in theice profiles from source to source are identified. It is found thatexcellent fits to all the spectra can be obtained using aphenomenological decomposition of the CO stretching vibration profile at4.67 μm into 3 components, centered on 2143.7 cm-1, 2139.9cm-1 and 2136.5 cm-1 with fixed widths of 3.0, 3.5and 10.6 cm-1, respectively. All observed interstellar COprofiles can thus be uniquely described by a model depending on only 3linear fit parameters, indicating that a maximum of 3 specific molecularenvironments of solid CO exist under astrophysical conditions. A simplephysical model of the CO ice is presented, which shows that the 2139.9cm-1 component is indistinguishable from pure CO ice. It isconcluded, that in the majority of the observed lines of sight, 60-90%of the CO is in a nearly pure form. In the same model the 2143.7cm-1 component can possibly be explained by the longitudinaloptical (LO) component of the vibrational transition in pure crystallineCO ice which appears when the background source is linearly polarised.The model therefore predicts the polarisation fraction at 4.67 μm,which can be confirmed by imaging polarimetry. The 2152 cm-1feature characteristic of CO on or in an unprocessed water matrix is notdetected toward any source and stringent upper limits are given. Whenthis is taken into account, the 2136.5 cm-1 component is notconsistent with the available water-rich laboratory mixtures and wesuggest that the carrier is not yet fully understood. A shallowabsorption band centered between 2165 cm-1 and 2180cm-1 is detected towards 30 sources. For low-mass stars, thisband is correlated with the CO component at 2136.5 cm-1,suggesting the presence of a carrier different from XCN at 2175cm-1. Furthermore the absorption band from solid13CO at 2092 cm-1 is detected towards IRS 51 inthe rho Ophiuchi cloud complex and an isotopic ratio of12CO/13CO=68+/-10 is derived. It is shown that allthe observed solid 12CO profiles, along with the solid13CO profile, are consistent with grains with an irregularlyshaped CO ice mantle simulated by a Continuous Distribution ofEllipsoids (CDE), but inconsistent with the commonly used models ofspherical grains in the Rayleigh limit.Based on observations obtained at the European Southern Observatory,Paranal, Chile, within the observing programs 164.I-0605 and 69.C-0441.ISO is an ESA project with instruments funded by ESA Member States(especially the PI countries: France, Germany, The Netherlands and theUK) and with the participation of ISAS and NASA.Table \ref{SourceList} and Appendices A and B are only available inelectronic form at http://www.edpsciences.org
| Revisiting the solid HDO/H2O abundances
We revisit the reported detection and upper limits on HDO in ice mantlespresent in the molecular cloud environments of the massive youngprotostars Gl 2136 and W33 A, using independent VLT-ISAAC and UKIRT-CGS4spectroscopic observations. We also present VLT and UKIRT spectra ofRAFGL 7009 near the HDO absorption wavelength and reanalyze the ISO-SWSspectral data for NGC 7538 IRS9, Orion-BN and S140. We demonstrate thatthe previously reported detections of HDO in W33 A and NGC 7538 IRS9 areincorrect. We present an in-depth analysis that shows that, besides thesensitivity limits, detection of low levels of HDO is difficult inamorphous ice mantles when features from solid methanol, a common grainmantle constituent, are present. We discuss the specific problemsarising in the ISO data in this wavelength range for NGC 7538 IRS9.Using VLT-ISAAC observations, we also investigate the HDO/H2Oratio toward the intermediate mass stars IRAS 05329-0728 and IRAS08448-4343. Our derived upper limits for the D/H ratio in water icerange from HDO/H2O < 1% to 0.2% in the different sources,and we discuss these limits in comparison with values derived in otherenvironments.Based on observations collected at the European Southern Observatory,Paranal, Chile (ESO Programme 164.I-0605(A)), UKIRT, Mauna Kea, Hawaii,and ISO satellite. The United Kingdom Infrared Telescope is operated bythe Joint Astronomy Centre on behalf of the UK Particle Physics andAstronomy Research Council. TRG's research is supported by the GeminiObservatory, which is operated by the Association of Universities forResearch in Astronomy, Inc., on behalf of the international Geminipartnership of Argentina, Australia, Brazil, Canada, Chile, the UK, andthe USA.
| Observations of H3 in the Diffuse Interstellar Medium
Surprisingly large column densities of H+3 havebeen detected using infrared absorption spectroscopy in seven diffusecloud sight lines (Cygnus OB2 12, Cygnus OB2 5, HD 183143, HD 20041, WR104, WR 118, and WR 121), demonstrating that H+3is ubiquitous in the diffuse interstellar medium. Using the standardmodel of diffuse cloud chemistry, our H+3 columndensities imply unreasonably long path lengths (~1 kpc) and lowdensities (~3 cm-3). Complimentary millimeter-wave, infrared,and visible observations of related species suggest that the chemicalmodel is incorrect and that the number density ofH+3 must be increased by 1-2 orders of magnitude.Possible solutions include a reduced electron fraction, an enhanced rateof H2 ionization, and/or a smaller value of theH+3 dissociative recombination rate constant thanimplied by laboratory experiments.
| Speckle Interferometry at the US Naval Observatory. VIII.
The results of 2044 speckle interferometric observations of doublestars, made with the 26 inch (66 cm) refractor of the US NavalObservatory, are presented. Each speckle interferometric observation ofa system represents a combination of over a thousand short-exposureimages. These observations are averaged into 1399 mean positions andrange in separation from 0.16" to 14.97", with a mean separation of2.51". This is the eighth in a series of papers presenting measuresobtained with this system and covers the period 2001 March 18 through2001 December 30.
| Detection of abundant solid CO in the disk around CRBR 2422.8-3423
We present direct evidence for CO freeze-out in a circumstellar diskaround the edge-on class I object CRBR 2422.8-3423,observed in the M band with VLT-ISAAC at a resolving power R~ 10 000.The spectrum shows strong solid CO absorption, with a lower limit on thecolumn density of 2.2 x 1018 cm-2. The solid COcolumn is the highest observed so far, including high-mass protostarsand background field stars. Absorption by foreground cloud materiallikely accounts for only a small fraction of the total solid CO, basedon the weakness of solid CO absorption toward nearby sources and theabsence of gaseous C18O J=2-> 1 emission 30\arcsec south.Gas-phase ro-vibrational CO absorption lines are also detected with amean temperature of 50 +/- 10 K. The average gas/solid CO ratio is ~ 1along the line of sight. For an estimated inclination of 20degr +/-5°, the solid CO absorption originates mostly in the cold, shieldedouter part of the flaring disk, consistent with the predominance ofapolar solid CO in the spectrum and the non-detection of solidOCN-, an indicator of thermal/ultraviolet processing of theice mantle. By contrast, the warm gaseous CO likely originates closer tothe star. Based on observations obtained at the European SouthernObservatory (ESO), Paranal, Chile, within the observing program164.I-0605.}
| The interstellar extinction to V4334 Sgr (Sakurai's object)
We present an 8-13 mu m spectrum of V4334 Sgr (Sakurai's object), whichshows clear evidence for the presence of a silicate absorption featureat 9.7 mu m. We argue that the feature is interstellar in origin, and onthis basis we determine the interstellar extinction to V4334 Sgr to beE(B-V)=0.66+/-0.12. This is the only determination of the extinction toV4334 Sgr to date that uses direct observation of the interveningmaterial; as the reddening using this method is refined it will be ofimportance in determining the distance of V4334 Sgr, and hence inmodelling its evolution.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| Do dusty A stars exhibit accretion signatures in their photospheres?
We determined abundances of O, Ca, Fe, Ba and Y for a sample of dustyand dust-free A stars, taken from the list of Cheng et al.(\cite{Cheng92}). Five of the stars have an infrared-excess due tocircumstellar dust. Ongoing accretion from their circumstellarsurroundings might have modified the abundances in the photospheres ofthese stars, but our results clearly show, that there is no differencein the photospheric composition of the dusty and dust-free stars.Instead all of them show the typical diffusion pattern which diminishestowards larger rotational velocities.
| A revised HRD for individual components of binary systems from BaSeL BVRI synthetic photometry. Influence of interstellar extinction and stellar rotation
Johnson BVRI photometric data for individual components of binarysystems have been provided by ten Brummelaar et al. (\cite{Brummelaar}).This is essential because non-interacting binaries can be considered astwo single stars and therefore play a critical role in testing andcalibrating single-star stellar evolution sets of isochrones and theimplicit theory. While they derived the effective temperature (T_eff)from their estimated spectral type, we infer metallicity-dependent T_efffrom a minimizing method fitting the B-V, V-R and V-I colours. For thispurpose, a grid of 621 600 flux distributions were computed from theBasel Stellar Library (BaSeL 2.2) of model-atmosphere spectra, and theirtheoretical colours compared with the observed photometry. The BaSeLcolours show a very good agreement with the BVRI metallicity-dependentempirical calibrations of Alonso et al. (\cite{Alonso}), with thetemperatures being different by 3+/-3% in the range 4000-8000 K fordwarf stars. Before deriving the metallicity-dependent T_eff from theBaSeL models, we paid particular attention to the influence of reddeningand stellar rotation. We inferred the reddening from two differentmethods: (i) the MExcessNg code v1.1 (Méndez & van Altena\cite{Mendez}) and (ii) neutral hydrogen column density data. Acomparison of both methods shows a good agreement for the sample locatedinside a local sphere of ~ 500 pc, but we point out a few directionswhere the MExcess model overestimates the E(B-V) colour excess.Influence of stellar rotation on the BVRI colours can be neglectedexcept for 5 stars with large v sin i, the maximum effect on temperaturebeing less than 5%. Our final determinations provide effectivetemperature estimates for each component. They are in good agreementwith previous spectroscopic determinations available for a few primarycomponents, and with ten Brummelaar et al. below ~ 10 000 K.Nevertheless, we obtain an increasing disagreement with theirtemperatures beyond 10 000 K. Finally, we provide a revisedHertzsprung-Russell diagram (HRD) for the systems with the moreaccurately determined temperatures.
| High Spectral and Spatial Resolution Observations of Shocked Molecular Hydrogen at the Galactic Center
The presence of OH (1720 MHz) masers and the absence of counterparts at1665/1667 MHz has proved to be a clear diagnostic of shocked moleculargas associated with Galactic supernova remnants. This suggests thatshocked molecular gas should be associated with the OH (1720 MHz) masersthat have been detected in the circumnuclear disk (CND) and Sgr A Eastat the Galactic center. In order to test this hypothesis, we observedthe H2 1-0 S(1) and Brγ lines using NICMOS on theHubble Space Telescope (HST) and the University of New South WalesInfrared Fabry-Perot (UNSWIRF) etalon at the Anglo-Australian Telescope(AAT), near the regions where OH (1720 MHz) masers are detected in theCND and Sgr A East. We present the distribution of H2 in thenorth and south lobes of the CND and in Sgr A East. H2emission accompanies almost all the maser spots detected at the Galacticcenter. In particular, we find a striking filamentary structure near thenorthwest of the CND and evidence that shocked molecular gas isassociated with the 70 km s-1 molecular cloud at the Galacticcenter. We argue that the emission from the CND could arise in gasheated by the dissipation of the random motion of clumps by collisionsor the dissipation of turbulence in a more homogeneous medium. Inaddition, highly redshifted gas of up to 140 km s-1 close tothe eastern edge of the Sgr A East shell is detected. These observationscombined with OH (1720 MHz) results suggest that the H2 gasis shocked and accelerated by the expansion of Sgr A East into the 50and the 70 km s-1 clouds and into the lobes of the CND.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Speckle Interferometry at the US Naval Observatory. VI.
The results of 1068 speckle interferometric observations of doublestars, made with the 26 inch (0.66 m) refractor of the US NavalObservatory, are presented. These observations are averaged into 841means of 815 binary stars. The systems range in separation from 0.22" to6.01" with a mean separation of 2.21" and have a limiting secondarymagnitude of V=12.5. This is the sixth in a series of papers presentingmeasures obtained with this system, and it covers the period 1999January 1 through 2000 January 9.
| ICCD Speckle Observations of Binary Stars. XXIII. Measurements during 1982-1997 from Six Telescopes, with 14 New Orbits
We present 2017 observations of 1286 binary stars, observed by means ofspeckle interferometry using six telescopes over a 15 year period from1982 April to 1997 June. These measurements constitute the 23dinstallment in CHARA's speckle program at 2 to 4 m class telescopes andinclude the second major collection of measurements from the MountWilson 100 inch (2.5 m) Hooker Telescope. Orbital elements are alsopresented for 14 systems, seven of which have had no previouslypublished orbital analyses.
| Speckle Interferometry at the US Naval Observatory. V.
The results of 1544 speckle interferometric observations of 637 binarystars, ranging in separation from 0.25" to 5.25", are tabulated. Theseobservations were obtained using the 66 cm refractor at the US NavalObservatory in Washington, DC, with an intensified CCD detector. This isthe fifth in a series of papers presenting measures obtained with thissystem and covers the period 1998 January 1 through December 31. Randomerrors for all measures are estimated to be 17.6 mas in separation and0.55d/ρ in position angle, where ρ is the separation inarcseconds.
| Binary Star Differential Photometry Using the Adaptive Optics System at Mount Wilson Observatory
We present photometric and astrometric results for 36 binary systemsobserved with the natural guide star adaptive optics system of the MountWilson Institute on the 100 inch (2.5 m) Hooker Telescope. Themeasurements consist of differential photometry in U, B, V, R, and Ifilters along with astrometry of the relative positions of systemcomponents. Magnitude differences were combined with absolute photometryfound in the literature of the combined light for systems to obtainapparent magnitudes for the individual components at standardbandpasses, which in turn led to color determinations and spectraltypes. The combination of these results with Hipparcos parallaxmeasurements yielded absolute magnitudes and allowed us to plot thecomponents on an H-R diagram. To further examine the reliability andself-consistency of these data, we also estimated system masses from thespectral types. Based on observations made at Mount Wilson Observatory,operated by the Mount Wilson Institute under an agreement with theCarnegie Institution of Washington.
| Spectroscopy of molecular hydrogen in outflows from young stars
We present new medium-resolution longslit spectra in the near-infraredand examine the excitation of molecular hydrogen across several outflowsfrom young stars. In contrast to previous studies, in which thebrightest patches in the flows were selected, we find evidence forvariations in excitation with position within several sources. Wepresent and comment on a number of H_2 excitation mechanisms of outflowsfrom the literature, and compare them with our observations. H_2position-velocity diagrams and line ratios support a picture in whichthe excitation variations are caused by the large-scale shock geometry.The variations are best interpreted by magnetohydrodynamic C-shocks,although some locations which demonstrate hydrodynamic J-type excitationare found. In particular, VLA 1623 is accuratelymodelled by a C-type bow, whereas a planar J-type model is favoured forHH 57. HH 1/2 consists of acollection of molecular bow and planar shocks. The H_2 emission from theleading edge of the HH 1 bow structure is actuallyfrom a low-excitation oblique wing from one of many mini bow shocksrather than from fluorescence or a magnetic precursor. In two of ourobjects, the jets themselves are also traced in molecular hydrogenemission. Radial velocities in the infrared jet in HH 47C demonstrateacceleration consistent with the proper motions, and hint at ballisticmotions originating in an eruptive event about 280 years ago. In thisjet, as well as in the HH 1 infrared jet, we find theexcitation to decline with distance from the source. Based onobservations collected at the European Southern Observatory, La Silla,Chile.
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| Observations of H^+_3 in Dense Molecular Clouds
H^+_3 has been detected using infrared absorption spectroscopy along thelines of sight to six infrared sources in dense molecular clouds: AFGL2136, W33A, Mon R2 IRS 3, AFGL 961E, AFGL 2591, and AFGL 490. Upperlimits to the column densities of H^+_3 are reported for an additionalnine sources. The column densities of CO toward Mon R2 IRS 3 and AFGL961E have been determined from observations of the first-overtone linesof CO. For the six sources toward which H^+_3 was detected, a simplemodel of H^+_3 chemistry has been used together with column densities ofH_2 derived from infrared CO measurements to estimate column lengths,mean number densities, and temperatures of molecular clouds. The derivedcolumn lengths are on the order of a parsec, the number densities are10^4-10^5 cm^-3, and the temperatures are ~25-50 K.
| Speckle Interferometry at the US Naval Observatory. IV.
The results of 1314 speckle interferometric observations of 625 binarystars, ranging in separation from 0.2" to 5.2" with a limiting secondarymagnitude of V=11, are tabulated. These observations were obtained usingthe 66 cm refractor at the US Naval Observatory in Washington, DC, withan intensified CCD detector. This is the fourth in a series of paperspresenting measures obtained with this equipment and covers the period1997 January 1 through December 31. Random errors for all measures areestimated to be 18 mas in separation and 0.57d/rho in position angle,where rho is the separation in arcseconds.
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| Speckle Interferometry at the US Naval Observatory. III.
Position angles and separations resulting from 2578 speckleinterferometric observations of 590 binary stars are tabulated. This isthe third in a series of papers presenting measures obtained using the66 cm refractor at the US Naval Observatory in Washington, DC, andcovers the period from 1995 June through 1996 December. Program starsrange in separation from 0.2" to 4.3", with a limiting magnitude ofV=11. Random errors are estimated to be 17.0 mas in separation and0.56d/rho in position angle, where rho is the separation in arcseconds.These are the first results acquired using an improved intensified CCDdetector. The new detector, in concert with an intensity-filteringtechnique applied in software, has permitted a 1 mag increase in dynamicrange, to 3.5 mag, for pairs separated by about 2". The instrumentationand calibration are briefly described, with an emphasis on thecharacteristics of the new detector. The software filter used toincrease the dynamic range is also described.
| Speckle Interferometry at the US Naval Observatory. II.
Position angles and separations resulting from 2406 speckleinterferometric observations of 547 binary stars are tabulated. This isthe second in a series of papers presenting measures obtained using the66 cm refractor at the US Naval Observatory in Washington, DC, with anintensified CCD detector. Program stars range in separation from 0.2" to3.8", with Deltam<=2.5 mag and a limiting magnitude of V=10.0. Theobservation epochs run from 1993 January through 1995 August. Randomerrors are estimated to be 14 mas in separation and 0.52d/rho inposition angle, where rho is the separation in arcseconds. Theinstrumentation and calibration are briefly described. Aspects of thedata analysis related to the avoidance of systematic errors are alsodiscussed.
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | נושא הנחש |
| התרוממות ימנית: | 17h10m22.70s |
| סירוב: | -15°43'29.0" |
| גודל גלוי: | 2.43 |
| מרחק: | 25.793 פארסק |
| תנועה נכונה: | 0 |
| תנועה נכונה: | 0 |
| B-T magnitude: | 2.597 |
| V-T magnitude: | 2.477 |
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