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Magnetic fields in the nearby Universe, as observed in solar and planetary realms, stars, and interstellar starforming nurseries
Here I present a survey of planetary, stellar and clumpy interstellarmagnetic fields, with an emphasis on discoveries made in the lastdecade. Ground-based and Earth-satellite observations of magneticfields in astronomical objects are cataloged, as obtained at allmultiple electromagnetic wavelengths.For each type of object, the basicobservational properties are summarized, and the best theoreticalscenario which accounts for the large body of observations is discussed.There is no single unifying magnetic model for all objects (althoughdynamo theory comes close for many compact objects, and helical theoryfor many extended objects).The strength of the observed magnetic fieldsreaches exagauss values (1018 G) in compact objects such asmagnetars, and decreases to microgauss values (10-6 G)in the clumpy interstellar medium.
| Variations in D/H and D/O from New Far Ultraviolet Spectroscopic Explorer Observations
We use data obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) to determine the interstellar abundances of D I, N I, O I, Fe II,and H2 along the sight lines to WD 1034+001, BD +39 3226, andTD1 32709. Our main focus is on determining the D/H, N/H, O/H, and D/Oratios along these sight lines, with logN(H)>20.0, that probe gaswell outside of the Local Bubble. Hubble Space Telescope (HST) andInternational Ultraviolet Explorer (IUE) archival data are used todetermine the H I column densities along the WD 1034+001 and TD1 32709sight lines, respectively. For BD +39 3226, a previously published N(HI) is used. We find(D/H)×105=2.14+0.53-0.45,1.17+0.31-0.25, and1.86+0.53-0.43 and(D/O)×102=6.31+1.79-1.38,5.62+1.61-1.31, and7.59+2.17-1.76 for the WD 1034+001, BD +39 3226,and TD1 32709 sight lines, respectively (all 1 σ). The scatter inthese three D/H ratios exemplifies the scatter that has been found byother authors for sight lines with column densities in the range19.2
| 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.
| Discovery of magnetic fields in hot subdwarfs
We present polarisation measurements of sdB and sdO stars using FORS1 onthe VLT. The observations were made as part of a project to determinewhether magnetic fields in two super-metal-rich stars can explain theirextreme abundance peculiarities. Field strengths of up to ~1.5 kG rangehave been measured at varying levels of significance in each of our sixtargets, however no clear evidence was found between apparently normalsubdwarfs and the metal-rich objects. The origin of the magnetic fieldsis unknown. We also discuss the implications of our measurements formagnetic flux conservation in late stages of stellar evolution.
| The Deuterium-to-Oxygen Ratio in the Interstellar Medium
Because the ionization balances for H I, O I, and D I are lockedtogether by charge exchange, the deuterium-to-oxygen ratio, D/O, is animportant tracer for the value of the D/H ratio and for potentialspatial variations in the ratio. As the D I and O I column densities areof similar orders of magnitude for a given sight line, comparisons ofthe two values will generally be less subject to systematic errors thancomparisons of D I and H I, which differ by about 5 orders of magnitude.Moreover, D/O is additionally sensitive to astration, because as starsdestroy deuterium, they should produce oxygen. We report here theresults of a survey of D/O in the interstellar medium performed with theFar Ultraviolet Spectroscopic Explorer. We also compare these resultswith those for D/N. Together with a few results from previous missions,the sample totals 24 lines of sight. The distances range from a few to~2000 pc and logN(D I) from ~13 to ~16 cm-2. The D/O ratio isconstant in the local interstellar medium out to distances of ~150 pcand N(DI)~=1×1015 cm-2, i.e., within theLocal Bubble. In this region of the interstellar space, we findD/O=(3.84+/-0.16)×10-2 (1 σ in the mean). Thehomogeneity of the local D/O measurements shows that the spatialvariations in the local D/H and O/H must be extremely few, if any. Acomparison of the Local Bubble mean value with the few D/O measurementsavailable for low-metallicity quasar sight lines shows that the D/Oratio decreases with cosmic evolution, as expected. Beyond the LocalBubble, we detected significant spatial variations in the value of D/O.This likely implies a variation in D/H, as O/H is known to not varysignificantly over the distances covered in this study. Our data setsuggests a present-epoch deuterium abundance below1×10-5, i.e., lower than the value usually assumed,around 1.5×10-5.
| 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.
| Standard stars: CCD photometry, transformations and comparisons
We discuss variations of the atmospheric extinction coefficients andtransformation equations to the standard UBVRI system based onobservations of standard stars during 1996-97 at Siding SpringObservatory using a thinned SITe CCD and coloured glass filters. In thetransformation from the initial natural system to the Landolt version ofthe standard system, a large nonlinear term related to the Balmerdiscontinuity was required for the U transformation. We then modifiedthe U filter, and the subsequent transformation to the SAAO version ofthe standard UBVRI system had only small nonlinear correction terms forU, B, and I. The correction terms relating to U and B are evidently dueto the Balmer discontinuity, while that relating to I seems to be due tothe Paschen discontinuity at a wavelegth of approximately 8200 Å.We also compared the results with Landolt's observations, and confirmedthe difference between the two sets of standard stars (SAAO andLandolt).
| The distribution of bright OB stars in the Canis Major-Puppis-Vela region of the Milky Way
The picture of the young stellar groups in the Canis Major-Puppis-Vela(215 deg
| Strömgren and Hβ photometry of O and B type stars in star-forming regions. I. Canis Major - Puppis - Vela
Strömgren and Hβ photometry of OB-stars generally brighterthan 9.5 mag in the Canis Major - Puppis - Vela region of Milky Way isreported. The observations are based on the Milky Way luminous-star (LS)identifications and are designed to create a complete, magnitude-limitedsample of LS for this field. We present new uvby photometry for 127 LSand Hβ photometry for 25 of them. These observations are part of anongoing effort to improve the completeness of the existing uvbybetadata-base for the bright OB-type stars in the Milky Way, with the aim toinvestigate the structure of selected star-forming regions. Based ondata from the Strömgren Automatic Telescope of the CopenhagenAstronomical Observatory, La Silla. Tables 3 and 4 are only available inelectronic form at the CDS via anonymous ftp to 130.79.128.5 or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Spectrophotometry: Revised Standards and Techniques
The telluric features redward of 6700 Å have been removed from theaccurate spectrophotometric standards of Hamuy et al. to permit morereliable relative and absolute spectrophotometry to be obtained from CCDspectra. Smooth fluxes from 3300 to 10500 Å are best determined bydividing the raw spectra of all objects taken in a night by the rawspectrum of a ``smooth'' spectrum star before deriving the instrumentalresponse function using the revised standard star fluxes. In this waythe telluric features and any large instrumental variation withwavelength are removed from the raw data, leaving smooth spectra thatneed only small corrections to place them on an absolute flux scale.These small corrections with wavelength are well described by alow-order polynomial and result in very smooth flux-calibrated spectra.
| 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.
| Supplementary southern standards for UBV(RI)c photometry
We present UBV(RI)c photometry for 80 southern red and blue stars foruse as additional standards. The data are tied to the Johnson UBV andCousins (RI)c systems and extend the range of the available stars forcolor equation determination, especially in (U-B) for blue stars and(V-R) and (V-I) for red stars. Comparisons with published data are madeand particularly good agreement is found with Bessell for the red(Gliese) stars.
| Metal abundances in subdwarf O stars.
We describe a non-LTE analysis of seven subdwarf O stars and fourcentral stars of planetary nebulae. The analysis yields metal abundances(or upper limits to these) of C, N, O, Mg, Al, and Si for most of thesestars. Also effective temperature, surface gravity and helium abundancewere determined for those programme stars for which no reliableestimates of these parameters were available. The derived abundancepatterns prove to be disparate. We also compare the sdO stars in oursample with other sdO analyses (18 object in total) and find that thisstellar class is not homogeneous with respect to metal abundances. Atentative subclassification according to helium content andluminosity-to-mass ratio indicates that the compact, high-gravity sdOstars have similar metal abundances with a strong signature of hydrogenburning in the CNO cycle. They only differ in the amounts of helium andcarbon present in the photosphere, probably caused by varyingefficiencies of mixing or surface erosion. Luminous sdOs, on the otherhand, show markedly different metallicities, suggesting differentorigins. The star CPD-31 1701 is identified as a peculiar object. Ascompared with other O subdwarfs with nearly identical parameters, itsHe^44^Sc II line profiles appear shallow and rounded, lacking a welldefined core. They can also not be fitted by theoretical profiles. Noexplanation for this discrepancy could be found yet. Our analysis yieldsmicroturbulence velocities in the range 0-10km/s for all stars with asufficient number of metal lines. No indication was found for highervalues like the 20km/s reported by Hubeny et al. (1991) for the sdO starBD+75 325.
| A spectroscopic database for Stephenson-Sanduleak Southern Luminous Stars
A database of published spectral classifications for objects in theStepenson-Sanduleak Luminous Stars in the Southern Milky Way catalog hasbeen compiled from the literature. A total of 6182 classifications for2562 stars from 139 sources are incorporated.
| Complementarity between photometry and spectroscopy.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994RMxAA..29..111G&db_key=AST
| NLTE-analysis of subluminous O stars - KS 292
High-resolution spectra of the southern Galactic sdO star KS 292 areanalyzed using modern NLTE model atmospheres in order to determine theatmospheric parameters. The results indicate that KS 292 probablybelongs to a newly discovered group of post-AGB stars which arecharacterized by effective temperatures and gravities typical forcentral stars of planetary nebulae but which apparently lackcircumstellar nebulae.
| Broad-band photometry of selected southern ultraviolet-bright stars.
Not Available
| Radial velocities and spectral types for a sample of faint blue stars.
Not Available
| A catalogue of spectroscopically identified hot subdwarf stars.
Not Available
| Southern Hemisphere Spectrophotometric Standards
Not Available
| Photometry of faint blue stars. IV - Some 'very definitely blue' PHL stars
Photometry on the uvby system is presented for 56 faint blue stars,mostly from the Palomar-Haro-Luyten 'very definitely blue' list. Themajority of these stars are hot subdwarfs.
| P Cygni and related profiles in the ultraviolet spectra of O-stars
P Cygni and related profiles of the resonance lines of N V, Si IV and CIV ions are studied over a sample of 40 O-stars observed with IUE in thehigh resolution mode. The sample includes subdwarf stars, highluminosity population II objects, stars which are not recognized membersof open clusters and/or associations, and stars which are members. Theprofiles give information on the ionization structure of the expandingstellar atmosphere and on the velocity fields. The large variety ofthese profiles and the wide range of observed velocities allow a look tobe taken at the largely unexplored field of stellar individuality.
| UBV photometry for southern OB stars
New UBV photometry of 1227 OB stars in the southern Milky Way ispresented. For 1113 of these stars, MK spectral types have been reportedpreviously in a comprehensive survey to B = 10.0 mag.
| A survey of ultraviolet objects
An all-sky survey of ultraviolet objects is presented together with astatistical analysis that leads to the conclusion that there is asignificantly higher population of hot subdwarfs lying below themain-sequence than hitherto thought. The distribution of all ultravioletobjects, main sequence ultraviolet objects, and MK unclassifiedultraviolet objects are shown in galactic coordinates, and the absolutemagnitudes and color-color diagrams for these groups are presented.Scale heights are derived, giving values similar to planetary nebulaefor the hottest groups.
| Different stellar winds in O-type stars
A progress report on the analysis of the IUE high-resolution, far-UVspectra of a sample of 29 O4-B0 and sdO stars is presented. Somemorphological properties of the N V wavelength 1238-1242 lines arementioned and, from a comparison with the C IV wavelength 1548-1551profiles, the possibility of different CNO abundance effects in thestellar sample is explored. For the stars in the sample, the HD and BDnumbers, the spectral types, the IUE image number, the OB association towhich the star probably belongs, and the maximum expansion velocity atwhich N V and C IV can be detected are listed. It is suggested that thepossible effects of CNO chemical abundance variations may explaindifferences in these maximum wavelength displacements. The CNO relativeabundance differences would be due to evolutionary effects that tend toincrease the nitrogen abundance with time.
| NON-LTE analysis of subluminous O-stars. IV - Spectral photometry and NLTE analysis of 11 subluminous stars
The spectra of 11 subluminous O-type stars were obtained with the ESO3.60 m telescope (a resolution of 29 A/mm at wavelengths of 4250-4800A). The spectra were analyzed quantitatively for effective temperature,surface gravity, and H/He ratio by using a grid of NLTE modelatmospheres, effective temperature from 36,000 to 55,000 K, and log gfrom 4.0 to 6.5. Seven of the stars are helium-enriched; two areextremely rich in helium (SB21 and TON-S 103). The evolutionary statusof the intermediate helium stars is examined.
| Spectral atlas of helium-rich stars
An atlas of coude spectra of 33 helium-rich O- and B-stars and 11comparison stars in the 3700-4600 A spectral range is presented. Theatlas comprises stars with temperatures from 10,000 to 60,000 deg K inwhich He lines are visible in the spectra, and includes variable Hestars; stars with spectral types O8 to B5 and magnitudes (m(v)) lessthan or equal to 11.0 are considered. The purpose of the atlas is togive a sample of spectra in which, from the observational point of view,the differences caused by certain physical parameters includingeffective temperature, logarithm of the gravity and observed rotationalvelocity, can be judged by eye. Mechanisms for He enrichment in theatmosphere are also discussed.
| SB 21, an extremely helium-rich subdwarf O-star
Spectral observations of the subdwarf O star SB 21 are reported. Theobservations were made at a dispersion of 29 A/mm in the spectral range4250-4800 A using a 3.6-m telescope and an image dissector scanner. TheH gamma line is found to be absent in SB 21, while the He I lines at4388, 4471 and 4713 A and the He II lines at 4686 and possibly 4542 aredetected. A detailed nonlocal thermodynamic equilibrium model analysisof the data indicates an effective temperature of 35,000 K, log g of 5.5and a He/H density ratio greater than 10. Differences between theextremely helium rich objects SB 21, CPD-31 1701 and BD + 48 177 andother extremely helium-rich objects such as BD +37 1877 and BD +37 442are pointed out.
| Photometric calibration of the International Ultraviolet Explorer /IUE/ - Low dispersion
Absolute sensitivity curves for IUE low-resolution spectra are obtainedby comparing IUE measurements of hot stars with the absolute energydistributions established for these objects by previous satellite androcket experiments. The differences between these earlier experimentsare discussed quantitatively, and a common absolute flux scale isproposed as the basis for the absolute calibration of IUE.
| On the 4430 A interstellar band - A visual classification
A system of visual classification of the strength of the interstellarband 4430 A has been developed, based on spectra taken at spectralclassification dispersion. The intensity of the band was divided into 8main classes, defined by a group of selected standard stars. The systemwas applied to 1,111 southern OB stars contained in the catalog ofspectral types by Garrison, Hiltner, and Schild (1977). The mean errorin the classification was estimated to be plus or minus 1 class.Equivalent widths were measured for 100 stars; an excellent correlationwith the visual estimations was obtained. A calibration between thesetwo parameters is given.
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| Сазвежђа: | Крма |
| Ректацензија: | 07h36m30.20s |
| Deклинација: | -32°12'43.7" |
| Apparent магнитуда: | 10.476 |
| Proper motion RA: | -24.6 |
| Proper motion Dec: | 37.4 |
| B-T magnitude: | 10.148 |
| V-T magnitude: | 10.449 |
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