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Small Magellanic Cloud-Type Interstellar Dust in the Milky Way
It is well known that the sight line toward HD 204827 in the clusterTrumpler 37 shows a UV extinction curve that does not follow the averageGalactic extinction relation. However, when a dust component, foregroundto the cluster, is removed, the residual extinction curve is identicalto that found in the SMC within the uncertainties. The curve is verysteep and has little or no 2175 Å bump. The position of HD 204827in the sky is projected onto the edge of the Cepheus IRAS bubble. Inaddition, HD 204827 has an IRAS bow shock, indicating that it may beembedded in dust swept up by the supernova that created the IRAS bubble.Shocks due to the supernova may have led to substantial processing ofthis dust. The HD 204827 cloud is dense and rich in carbon molecules.The 3.4 μm feature indicating a C-H grain mantle is present in thedust toward HD 204827. The environment of the HD 204827 cloud dust maybe similar to the dust associated with HD 62542, which lies on the edgeof a stellar wind bubble and is also dense and rich in molecules. Thissight line may be a Rosetta Stone if its environment can be related tothose in the SMC having similar dust.
| The total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The identification of the transient X-ray pulsar Cepheus X-4 with a Be/X-ray binary
We present long slit spectral (375-725 nm) observations of the proposedidentification of the transient 66s X-ray pulsar Cep X-4=3DGS2138+56.Spectra show features typical of Be/X-ray binaries. Superimposed on aweak emission from the IC 1396 nebula, strong Hα (4.5 nm EW) andHβ (0.3 nm EW) lines are seen in emission with the other Balmerlines in absorption. Significant interstellar absorption features arealso detected, including a strong Na I doublet (589 nm) and diffusebands at 443, 578 and 628 nm. From the shape of the continuum as well asthe lines present in the spectrum, a most probable spectral type ofB1-B2V is derived with a reddening of E_{B-V}=3D1.3+/-0.1. The reddeningvalue is corroborated by the measure of interstellar absorptionfeatures, except for the sodium line which appears to be in excess andmay be partly from circumstellar origin. The optical absorption is fullyconsistent with the column density derived from X-ray spectra, thereforeconfirming the identification. Despite apparent spatial coincidence, thesource is located much further away than the local intervening nebulaIC1396. The best estimate of the distance is D=3D(3.8+/-0.6) kpc, whichplaces the source in the outer Perseus arm of the Galaxy. At thisdistance, the X-ray quiescent luminosity is (3-6) 10(33) erg.s(-1) ,thus comparable to typical Be/X-ray binary low states. Based onobservations collected at the Observatoire de Haute-Provence, CNRS,France
| Dust properties in the direction of Trumpler 37.
The fourteen brightest OB stars of the Trumpler 37 Cluster have beenobserved in the V,R,I,J,H,K photometric bands. These have been used toderive accurate measurements of the quantity R_V_=A_V_/E(B-V). Differentfrom previous studies it is found that in Trumpler 37 isclose to the mean interstellar value of 3.1. Most of the reddeningtowards Trumpler 37 is found to be of foreground origin. This isconsistent with the lack of variations, observed by us, of R_V_ with theprojected distance from the center of the cluster. In two highlyreddened stars of the cluster, whose reddening is certainly mostlylocal, the observed R_V_ is lower than the mean interstellar value of3.1. This is to be compared with the behaviour of the Trapezium stars inOrion, whose R_V_ is quite above such value whereas the age of thecluster is similar to the one of Trumpler 37.
| The X-ray view of the central part of IC 1396.
The galactic HII region IC 1396 contains one of the youngest known openstar clusters Trumpler 37, Tr 37. Its very core hosts the multipleO-star system HD 206267, which in many respects is similar to the OrionTrapezium. So far X-ray emission has been observed only from HD 206267with the Einstein observatory. Soft X-ray observations with the ROSATPSPC revealed X-ray emission from an area of 30' radius around thecenter of globule IC 1396A, which was resolved into 85 discrete sources.Some of the emission still remains unresolved. Most of the detectedX-ray sources, except HD 206267, are very weak, which causes themeasured luminosity function to be cut off at log L_x_<30.3(erg/s).X-ray sources are located not only in Tr 37 but are also scatteredaround the molecular globule IC 1396A. From the distribution of sources,their apparently hard spectra, and a steep luminosity function we arguethat this sample contains a large number of previously unknown low-massPMS stars. The X-ray source centered on HD 206267 appeared extendedindicating a multiple source system at the very center of Tr 37. Thetotal X-ray luminosity of the trapezium HD 206267 does compare with theX-ray luminosity of single O-type stars. We set an upper limit oflog(L_x_/L_bol_) to -6.90 and briefly discuss this result in the contextof colliding and eclipsing wind models in early type binaries.
| Absolute proper motions of the open clusters M 39 and TR 37
The absolute proper motions of five BD stars in the region of the opencluster M 39 and of 20 BD stars in the region of the open cluster Tr 37are determined with an accuracy of 0.26 arcsec/100 yr. Measurements ofthe proper motions of the open clusters M 39 and Tr 37 are reported.
| An Einstein Observatory SAO-based catalog of B-type stars
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
| Galactic OB associations in the northern Milky Way Galaxy. I - Longitudes 55 deg to 150 deg
The literature on all OB associations was reviewed, and their IRAS pointsource content was studied, between galactic longitude 55 and 150 deg.Only one third of the 24 associations listed by Ruprecht et al. (1981)have been the subject of individual studies designed to identify thebrightest stars. Distances to all of these were recomputed using themethod of cluster fitting of the B main sequence stars, which makes itpoossible to reexamine the absolute magnitude calibration of the Ostars, as well as for the red supergiant candidate stars. Also examinedwas the composite HR diagram for these associations. Associations withthe best defined main sequences, which also tend to contain very youngclusters, referred to here as OB clusters, have extremely few evolved Band A or red supergiants. Associations with poorly defined mainsequences and few OB clusters have many more evolved stars. They alsoshow an effect in the upper HR diagram referred to as a ledge byFitzpatrick and Garmany (1990) in similar data for the Large MagellanicCloud. It is suggested that the differences in the associations are notjust observational selection effects but represent real differences inage and formation history.
| Photometry of the young open cluster Trumpler 37
Photoelectric UBV observations of 120 stars in the young open clusterTrumpler 37 are presented, primarily in the magnitude range 10.0 - 13.5.An analysis of the color-magnitude diagram of the cluster yields an ageof 6.7 million yr and reveals the presence of a number of possiblepre-main-sequence stars in the cluster.
| The interstellar extinction law towards the open cluster TR-37
Near-infrared photometry of OB stars in the young open cluster TR-37 hasbeen obtained. These data have been combined with previous visual andultraviolet observations of the same sample and a detailed extinctioncurve has been derived, ranging from the near-infrared to thefar-ultraviolet. The extinction towards this sample of stars seems to beanomalous, consistent with a shift in the grain-size distribution withrespect to an average galactic extinction curve.
| Anomalous dust in the open cluster Trumpler 37
New IUE data were obtained towards stars in the open cluster Trumpler37. Extinction curves derived from these data show that the anomalousdust detected towards HD 204827 and HD 210072 is not unique to thoselines of sight but occurs generally in that region of the sky. The dustis apparently associated with the Trumpler 37 cluster, which forms thecenter of Cepheus OB2. This is a complex region of star formation wherethe evolution of dust grains through shock waves could be consideredlikely. A supernova in a slightly older star-forming region of Cep OB2located next to Trumpler 37 is a possible source of such a shock wave.
| Studies of luminous stars in nearby galaxies. I. Supergiants and O stars in the Milky Way.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978ApJS...38..309H&db_key=AST
| Some characteristics of the young open cluster Trumpler 37.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976PASP...88..865G&db_key=AST
| A Spectroscopic and Photometric Investigation of the Association Cepheus OB2
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968ApJ...154..923S&db_key=AST
| Determination of size, color indices, and spectral classes of stars in an area centered on R.A.=21h24m, Dec=+58.5deg.
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