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Early Infrared Spectral Development of V1187 Scorpii (Nova Scorpii 2004 No. 2)
We report on an unprecedented infrared time series of spectra of V1187Sco, a very fast ONeMg nova. The observations covered a 56 day period(2004 August 6-September 30) starting 2 days after the nova's peakbrightness. Time evolution of the spectra revealed changing linestrengths and profiles on timescales of less than a day to weeks as thenova evolved from early postmaximum to early coronal phases. When ourground-based optical and Spitzer Space Telescope data were combined, thewavelength coverage of 0.38-36 μm allowed an accurate spectral energydistribution to be derived when it was about 6 weeks after outburst.Developing double structure in the He I lines showed them changing fromnarrow to broad in only a few days. Using the O I lines in combinationwith the optical spectra, we derived a reddening of E(B-V)=1.56+/-0.08and a distance of 4.9+/-0.5 kpc. Modeling of the ejected materialstrongly suggested that it was geometrically thick withΔR/R=0.8-0.9 (more of a wind than a shell) and a low fillingfactor of order a few percent. The line shapes were consistent with acylindrical jet, bipolar, or spherical Hubble flow expansion with amaximum speed of about -3000 km s-1. The central peakappeared to be more associated with the spherical component, while thetwo peaks (especially in Hβ) suggested a ring with either a lowervelocity component or with its axis inclined to the line of sight.
| Far-Ultraviolet Stellar Photometry: Fields Centered on rho Ophiuchi and the Galactic Center
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..104..101S&db_key=AST
| The X-Ray Emission of A-Type Stars
From X-ray images in the ROSAT public archives, we determine soft X-rayfluxes, or flux upper limits, for 74 A-type stars, which have beenobserved during deep integrations with the PSPC. Nine supposedly single,late A stars (0.20 < B-V < 0.35) are found to coincide with X-raysources. The X-ray luminosities we infer for these stars range fromlevels comparable to the Active Sun, at log L_x ~27.6, to much brighteremission levels similar to those observed for active late-type binarysystems, near log L_x ~30.1. Another 10 sources are identified withearly A stars (0.0 < B-V < 0.2). Five of these are confirmeddouble stars, the rest are ostensibly single. The maximum luminosity wedetect in the early A stars, log L_x = 30.1, is 3.5 orders of magnitudebrighter than the X-ray upper limits for the nondetected stars.Additional study, including radial velocity monitoring and/or opticalinterferometry, will be needed to determine whether the putativelysingle X-ray emitting stars are in fact single, or whether theiremission is produced entirely or in part by unknown or unresolved binarycompanions. The level of X-ray emission associated with chemicallynormal, single A stars thus far appears to be uncorrelated with anyobvious stellar property, including the rotation rate, which is known togreatly influence the dynamo activity and the X-ray emission levels oflower mass stars. (SECTION: Stars)
| Far-ultraviolet stellar photometry: Fields in Sagittarius and Scorpius
Far-ultraviolet photometry for 741 objects in a field in Sagittariuscentered near M8 and 541 objects in a field centered near sigma Scorpiiis presented. These data were extracted from electographic imagesobtained with two cameras during a shuttle flight in 1991 April/May. Thecameras provided band passes with lambdaeff = 1375 A andlambdaeff = 1781 A. Synthetic colors show that these bandsare sensitive to effective temperature for hot stars. Our measurementswere placed on a quantitative far-ultraviolet magnitude scale byconvolving the spectra of stars observed by IUE with our cameras'spectral response functions. Fifty-eight percent of the ultravioletobjects were identified with visible stars using the SIMBAD databasewhile another 40% of the objects are blends of early type stars tooclose together to separate with our resolution. Our photometry iscompared with that from the TD-1, OAO 2, and ANS satellites and the S201(Apollo 16) far-ultraviolet camera and found to agree at the level of afew tenths of a magnitude. Unlike previous studies, almost half of theidentified visual counterparts to the ultraviolet objects are early Bstars. A plot of distance modulus against ultraviolet color excessreveals a significant population of stars with strong ultravioletexcess.
| AP stars with resolved magnetically split lines
New high-resolution spectroscopic observations of Ap stars with resolvedmagnetically split spectral lines are presented. Six new such stars havebeen discovered: HD 2453, HD 9996, HD 18078, HD 50169, HD 137949, and HD192678. This raises the total number of known Ap stars with resolvedmagnetically split lines to 21. The spectral line profiles observed intwo more stars, HD 111133 and HD 147010, are strongly affected by themagnetic field, but they are not fully resolved, due to nonnegligiblerotational Doppler effect. Observations of fairly sharp-lined Ap starswhose lines are unresolved are also presented. The relative differencebetween the equivalent widths of the Fe II lines 6147.7 A and 6149.2 Ais shown to increase with the mean magnetic field modulus. The existenceof a simple, unambiguous correlation between the mean magnetic fieldmodulus and the index Z of Geneva photometry, which had previously beenadvocated, is not confirmed. At most, stars with large negative valuesof Z may be more prone to have strong magnetic fields, but the evidencefor this is not statistically strong.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| AP stars with resolved Zeeman split lines
High-resolution, high SNR observations of a sample of sharp-lined Astars and of Ap stars showing resolved Zeeman split lines are presented.The Fe II lines 6147.7 A and 6149.2 A unexpectedly appear to beasymmetric in all stars where they are resolved. The blue component ofthe 6149.2 line, which is a Zeeman doublet, is deeper and narrower thanits red component. For line 6147.7, whose Zeeman pattern does not differmuch from a quadruplet, the red components are deeper than the blueones. It is shown that a partial Paschen-Back effect can account forthese properties. The potential implications of this finding for studiesof magnetic Ap stars are discussed.
| The magnetic field of the AM star Omicron Pegasi
Evidence is presented that the hot Am star Omicron Peg (= HD 214994) hasa magnetic field of the order of 2 kG, with a complex structure. Twoindependent approaches support this conclusion. The first one is ananalysis by the Stenflo-Lindegren (1977) technique of the widths of astatistical sample of lines. The other relies on a line-intensityanomaly that is found in magnetic stars. The implications of thisprobable detection of a field in a member of a class of stars that werenot previously known as magnetic is discussed.
| A photometric survey of the bright southern Be stars
Repeated UBV photometric measurements were made of the 86 bright Bestars south of declination -20 deg, and a network of comparison starswas set up. From a statistical study of the differential photometry itwas found that short- or intermediate-term variability seems to beoccurring in about half of the Be stars, and to be more evident in thestars of earlier spectral type. It was also possible to identify 11individual short- or intermediate-term variables. Four of these (all ofearly B spectral type) appear to exhibit significant variability on atime-scale of a day or less. More intensive observations of one of thesestars, 28 Omega CMA, indicate short-term variations consistent with thepublished spectroscopic period of 1.37 day.
| Evidence of decay of the magnetic fields of AP stars
Data obtained in the Geneva photometric system (Rufener, 1981) andappropriate calibrations of this system in terms of surface magneticfield and gravity are used to provide, on the basis of 708 field andcluster Ap stars, observational evidence that these stars undergo decayof their magnetic field on an evolutionary timescale. Justifications aregiven for the application of a photometric gravity calibration topeculiar stars. The dependence of the photometrically estimated surfacemagnetic field on gravity is found to differ markedly from availabletheoretical calculations. HgMn stars are found to show the same trend,strengthening the impression that they might be slightly magnetic.He-weak stars do not.
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