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Distribution of early type stars and dusty matter in the direction of the star cluster NGC 2175
The distribution of 120 O-B9-A2 stars and of the interstellar dust inthe direction of the star clusters NGC 2175 and NGC 2175s (the complexS252) is studied in terms of V, (B-V), and (U-B) data. Ten star groups(associations) are found at distances of 410, 720, 1000, 1500, 2200,3100, 4000, 5200, 7000, and 8100 pc. Three of these, at distances of410, 720, and 1000 pc, are type B associations. The remaining seven areOB associations. They are designated as Gem B 0.41, Gem B 0.72, Gem B1.0, Gem OB 1.5, Gem OB 2.2, Gem OB 3.1, Gem OB 4.0, Gem OB 5.2, Gem OB7.0, and Gem OB 8.1. The V absorption (AV) for stars No.2, 18, 20, 23,24, 26, 40, 41, 47, 69, 87, 88, 90, 95, 100 and 109 is estimated to be2m.78,4m.72, 2m.69, 3m.33, 2m.61, 2m.86, 4m.67, 6m.21, 3m.14, 3m.92,2m.69, 3m.04, 5m.95, 5m.95, 3m.20 and 5m.66, respectively. For most ofthese stars the absorption lies between 0m.5 and 2m.5. This largeabsorption may be caused by circumstellar absorption. The dust in theassociations Gem B 0.41 and Gem B 0.72 is distributed nonuniformly.There is no dust in the space between the associations. Essentiallythere is no dust inside those groups (associations) which lie atdistances greater than 1 kpc.
| BVRIJHK photometry of post-AGB candidates
BVRIJHK photometric observations are presented for 27 post-AGBcandidates. Almost all objects show a double peaked SED curve in theoptical to far-infrared wavelengths. Seventeen objects were classifiedas post-AGB stars on the basis of their spectral type, location in theIRAS color-color diagram and SED. The physical parameters of theobserved post-AGB stars, the inner radius of the detached shell, themass of the shell and the distance were derived using the simple dustshell model. We compared our observational sequence of post-AGB objectsto the theoretical evolutionary sequence (Schönberner\cite{schonberner1983}; Blöcker \cite{blocker}) in the stellartemperatures versus age diagram. We found that two post-AGB stars, IRAS05040+4820 and 08187-1905, have low stellar temperature with a largedynamical age of the dust shell. They appear to provide the firstobservational evidence that some low-mass stars bypass the planetarynebulae stage because of their slow increase in stellar temperature.Based on observations obtained at Kiso Observatory, Nagano, Japan.Table2 is also available 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/qcat?J/A+A/385/884
| Classification and properties of UV extinction curves
The catalog of Savage et al. (\cite{ref27}) reporting colour excesses of1415 stars from ANS photometry offers the opportunity to deeplyinvestigate the characteristics of UV extinction curves which differfrom the standard extinction of the diffuse interstellar medium. To thisaim we have selected a sample of 252 curves, which have been comparedwith the relations derived by Cardelli et al. (\cite{ref4}; CCM in thefollowing) for a variety of R_V values in the range 2.4-5 and have beenclassified as normal if they fit at least one of the CCM curves oranomalous otherwise. We find that normal curves with small R_V are justas numerous as those with large R_V. The anomalous objects are arrangedinto two groups according to the strength of the bump at 0.217 mu . Fora given value of c_2 this increases along the sequence: type Aanomalous, normals and type B anomalous, suggesting that this sequenceshould correspond to an increase of the amount of small grains along thesightline. Considerations concerning the environmental characteristicsindicate that the anomalous behaviour is not necessarily tied to theexistence of dense gas clouds along the line of sight.
| A survey of the 6.7 GHz methanol maser emission from IRAS sources. I. Data
We report the first results of a search for 6.7 GHz methanol masers inthe direction of 1399 IRAS objects north of declination-20deg with the flux densities greater than 100 Jy at 60 mu mand the flux density ratio F60/F25>1.Observations were made with the sensitivity of 1.7 Jy and the velocityresolution of 0.04 km s-1 using the 32-m Toruń radiotelescope. Maser emission was found in 182 sources, including 70 newdetections. 32 new sources were identified with objects of radioemission associated with star-forming regions. Comparison of the presentdata set with other observations suggests that about 65% of methanolmasers exhibit moderate or strong variations on time-scales of about 4and 8 years. Table 2 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Catalog of Visual Extinction Obtained from UV Color Excesses
Large collection of visual extinction A(V) and R_V equiv A_V/E(B-V)parameters for 1013 OB type stars is presented. The A(V) and R_V valueswere obtained from UV extinction curves. A comparison of obtained valueswith those obtained by Cardelli and Clayton (1991) from the near IRphotometry is also discussed.
| 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.
| A search for OH maser emission from post-asymptotic giant branch stars.
We present a survey for OH maser emission at 18cm in the direction of196 IRAS point sources. The primary aim of the survey was to detect OHmaser emission from post-asymptotic giant branch (post-AGB) stars. OHemission and/or absorption was detected in the direction of 77 sourcesof which 57 OH detections were previously unknown, giving an overalldetection rate of 39 per cent. Fourteen maser sources associated withevolved stars or planetary nebulae were found, corresponding to 7 percent of the total observed. These included three planetary nebulae (twonew OH detections), nine post-AGB stars (three new OH detections) andtwo cold OH/IR stars (both previously known). Two sources were ofuncertain identification (both new OH detections). The remainder of theOH sources were identified with young stellar objects and with HIIregions. The survey included the detection of OH maser emission from HD101584, an early-type supergiant at high Galactic latitude. For severalof the post-AGB stars, changes have occurred in the OH spectral profilesover a period of several years. This is interpreted as evidence forrapid changes in the stellar winds, due either to interactions withstellar companions, novae-like events or rapid stellar evolution.
| A CS(2-1) survey of IRAS point sources with color characteristics of ultra-compact HII regions.
We have made a complete survey of the CS(2-1) emission toward IRAS pointsources in the galactic plane. The sources observed were selectedaccording to their far infrared (FIR) colors, which are characteristicof UC HII regions. They have 25μm/12μm flux ratios larger than 3.7and 60μm/12μm flux ratios larger than 19.3. The survey covered aregion from b=-2deg to b=2deg from l=300deg to l=0deg and from l=0deg tol=60deg, and from b=-4deg to b=4deg elsewhere. We detected 843 sourcesout of 1427 sources observed. The distributions of detected andundetected sources in a FIR color-color diagram show some differences,suggesting that more than one type of object is present in our observedsample.
| Star Formation in the Gemini OB1 Molecular Cloud Complex
Abstract image available at:http://adsabs.harvard.edu/abs/1995ApJ...450..201C
| New detections of 5_1_-6_0_A^+^-methanol masers towards IRAS sources.
We present the results of our second search for 6.7-GHz methanol maserstowards colour-selected IRAS sources. Five hundred and twenty IRASsources that meet the far-infrared colour criteria set by Wood &Churchwell for ultra-compact HII regions were searched for 6.7-GHzmethanol maser emission, to a sensitivity limit of 5Jy. Thirty one newmaser sources were detected. We also compare the FIR colours of thenewly detected maser sources with those detected by Schutte et al.(1993) and the IRAS counterparts of sources that have both methanol andhydroxyl maser emission. It was found that the average flux distributionof the newly detected sources differs significantly from that of allother known 6.7-GHz methanol maser sources. It is argued that thedifferences may be due either to intrinsic differences between the threegroups of sources or to interstellar extinction. An analysis of therelation between the 6.7-GHz maser and IRAS flux densities shows thatthe maser flux density is always less than the 100 μm flux densitywhile only three sources have a maser flux density greater than the 60μm flux density. Far-infrared pumping of the 6.7-GHz methanol masersis therefore in principle viable although it was found that the apparentmaser efficiency will exceed 10 per cent for a significant number ofsources in the case of FIR pumping by photons between 50 and 100μm.The overall detection rates on the IRAS [25-12] vs [60-12] two-colourdiagram are also presented. Possible new search strategies for masers incolour-selected IRAS sources are discussed.
| UBVRI photometry and polarimetry of the stars in S252 (NGC 2175). II. Interpretation.
Photoelectric UBVRI photometry and polarimetry and photographic UBVRphotometry have been used to study the stellar cluster NGC2175associated with the Hii region-molecular cloud complex Sharpless252. Thecolour excess E_B-V_ of stars in NGC2175 ranges from the foregroundcolour excess of 0.4mag up to 1.7mag. The distance modulus of S252obtained by fitting ZAMS to the colour-magnitude diagrams of NGC2175 is11.7+/-0.3mag (2.2+/-0.3kpc). The lower part of the colour-magnitudediagrams of the main cluster contains stars still contracting towardsZAMS indicating an age of the order of one million years for thecluster. The age of a small subcluster to the east of the Hii region isa few million years. High stellar polarizations up to 12% have beenobserved. The average wavelength of the maximum polarization in S252 is0.53+/-0.01μm and the polarization efficiency is near the empiricalmaximum value 3A_v_. The polarization field in S252 is regular butcannot be explained by a single magnetic field direction.
| UBVRI photometry and polarimetry of the stars in S 252 (NGC 2175). I. The observations.
Photoelectric UBVRI photometry and polarimetry and photographic UBVRphotometry of stars in the direction of the galactic H II regionSharpless 252 are reported
| Tracing the Roots of Interstellar Mid Infrared Emission
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...275..549J&db_key=AST
| Environment Dependence of Interstellar Extinction Curves
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...274..439J&db_key=AST
| Infrared dust and millimeter-wave carbon monoxide emission in the Orion region
The far-infrared dust emission seen by the IRAS satellite in the Orionregion is analyzed as a function of the local radiation field intensity,and the dust temperature and opacity are compared with (C-12)O and(C-13)O emission. The infrared radiation is interpreted within theframework of a single-component large grain model and a multicomponentgrain model consisting of subpopulations of grains with size-dependenttemperatures. A strong dependence of the 100-micron optical depthderived is found using the large grain model on the averageline-of-sight dust temperature and radiation field. In the hotenvironment surrounding high-luminosity sources and H II regions, alldust along the line-of-sight radiates at 100 microns, and thedust-to-gas ratio, based on the 100-micron opacity and I(/C-13/O),appears to be in agreement with the standard value, about 1 percent bymass. A relationship is found between the inferred dust-to-gas ratio andthe radiation field intensity responsible for heating the dust which canbe used to estimate the gas column density from the dust opacity derivedfrom the 60- and 100-micron IRAS fluxes.
| Diffuse Infrared Emission of the S:252 HII Region - Molecular Cloud Complex
Not Available
| The relationship between infrared, optical, and ultraviolet extinction
The parameterized extinction data of Fitzpatrick and Massa (1986, 1988)for the ultraviolet and various sources for the optical andnear-infrared are used to derive a meaningful average extinction lawover the 3.5 micron to 0.125 wavelength range which is applicable toboth diffuse and dense regions of the interstellar medium. The lawdepends on only one parameter R(V) = A(V)/E(B-V). An analytic formula isgiven for the mean extinction law which can be used to calculate colorexcesses or to deredden observations. The validity of the law over alarge wavelength interval suggests that the processes which modify thesizes and compositions of grains are stochastic in nature and veryefficient.
| Multi-line observations and analysis of the Sharpless 247/252 gas complex
The 2.5 m antenna of the Observatoire de Bordeaux is used to map themolecular gas complex associated with the Sharpless 247/252 H II regionsin the J = 1-0 transition of C(O-13). The data show the existence of abridge between the S 247 S 252 molecular clouds as well of a complexkinematic structure. A search for OH masers at 18 cm was carried out inthe vicinity of the ionization front of the S 247 H II region and two OHmasers were found.
| The List of the Pairs of Stars with Different Light Absorptions in the Circumstellar Environments
Not Available
| An analysis of the shapes of ultraviolet extinction curves. II - The far-UV extinction
In this paper the properties of interstellar extinction in thefar-ultraviolet region are examined utilizing IUE extinction curves fora primary data sample of 45 reddened Milky Way OB stars. These resultsare combined with those derived for the 2175 A bump in a previous study.It is found that IUE extinction curves can be represented by linearcombinations of a Lorentzian-like 2175 A bump profile, a well-determinedFUV curvature term, and an underlying linear component. The parametersof the linear component are strongly correlated and therefore only fivefree parameters are required to fit all of the curves in our sample.Three parameters describe the 2175 A bump, one parameter describes thelinear background, and one parameter describes the strength of the FUVcurvature term. The shape of the FUV curvature is found to be identical,to within the observational errors, for all the curves in the sample -which spans virtually the entire range of extinction curve morphologiesobserved in the Milky Way.
| Atlas of the wavelength dependence of ultraviolet extinction in the Galaxy
The paper presents a collection of 115 extinction curves derived fromlow-dispersion IUE spectra. The spectra have been reduced with the useof techniques designed to reduce the effects of random noise and theinfluence of residual spectral features due to classification mismatch.The magnitudes of other instrumental and interpretational uncertaintiesare estimated. The extinction curves are presented with normalization toE(B-V) = 1 and the FUV portion (below 170 nm) is also shown for E(13-17)= 1. The atlas includes examples of extinction originating in thediffuse medium and several major nebulae and dense clouds.
| Observational constraints on the carriers of the ultraviolet extinction bump
Data from the Infrared Astronomical Satellite is used to investigate theorigin of the ultraviolet (UV) extinction bump. Correlations of the dusttemperature with the parameters of the UV bump, as derived from IUEobservations, are presented. Significant correlations of the 60/100brightness ratio with the area under the UV bump and the height of theUV bump are found. These last results suggest that the particlesresponsible for the UV bump are very sensitive to the strength of theradiation field. However, no significant correlation is found betweenthe dust temperature and the width of the UV bump, as would have beenexpected on the basis of recent physical models.
| Eight-colour photometry of stars associated with selected Sharpless H II regions at L exp II of about 190 deg - S 252, S 254, S 255, S 257, and S 261
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&A...171..216C&db_key=AST
| The interstellar 217 NM band - A third catalogue of equivalent widths
A catalog of equivalent widths of the 217 nm interstellar absorptionband as well as other parameters characterizing the extinction curve inthe ultraviolet has been compiled for 790 O and B stars. A relativelytight correlation between the equivalent width of the 217 nm band andE(B-V) indicates that the absorber of this band is connected with thepopulation of larger interstellar grains responsible for the visualextinction. The parameter characterizing the amount of extinction in thefar UV is only weakly correlated with E(B-V), a result in accord withthe assumption that a second population of very small grains causes therapid increase of the far-UV extinction.
| An analysis on the shapes of ultraviolet extinction curves. I - The 2175 A bump
IUE data are used to investigate the properties of the 2175 Ainterstellar extinction bump toward 45 reddened Milky Way stars. Usinganalytic fitting functions, parameters are derived which describe thecentral position, FWHM, and strength of the bump. The bump position isvery stable, with an extreme deviation which is still significantlylarger than the measurement uncertainty, indicating true variability.The bump FWHM has a large range of intrinsic values, 0.77/micron to1.25/micron. The normalized bump strength varies by more than a factorof three. There are no convincing correlations among the three bumpparameters, but the width of the bump is strongly correlated with thedust grain environments. Dense quiescent regions yield broad bumps,while diffuse interstellar medium and regions of recent star formationyield narrower bumps. The absence of any correlation between bump widthand central position argues strongly against graphite grains in the sizerange prescribed by the Mathis, Rumpl, and Nordsieck (1977) model ascarriers of the bump.
| A catalog of ultraviolet interstellar extinction excesses for 1415 stars
Ultraviolet interstellar extinction excesses are presented for 1415stars with spectral types B7 and earlier. The excesses with respect to Vare derived from Astronomical Netherlands Satellite (ANS) 5-channel UVphotometry at central wavelengths of approximately 1550, 1800, 2500, and3300 A. A measure of the excess extinction in the 2200-A extinction bumpis also given. The data are valuable for investigating the systematicsof peculiar interstellar extinction and for studying the character of UVinterstellar extinction in the general direction of stars for which theextinction-curve shape is unknown.
| O-B2-STARS with Large Circumstellar Obscuration
Not Available
| Exciting stars and the distances of the diffuse nebulae
Not Available
| Peculiar ultraviolet interstellar extinction
In connection with investigations of the physical characteristics ofinterstellar dust, a study of objects with peculiar extinction mightprovide new insights about the composition, size distribution,formation, and destruction of the particulate matter. Meyer and Savage(1981) have found that the dust toward many stars exhibits peculiar UVextinction. The present investigation is concerned with InternationalUltraviolet Explorer (IUE) spectrophotometric measurements for a sampleof stars judged by Meyer and Savage to have highly anomalous UVextinction as inferred from the broad-band Astronomical NetherlandsSatellite (ANS) data. The reported IUE measurements provide theopportunity to determine if the ANS photometry measurements of Meyer andSavage are anomalous because of peculiar extinction.
| IUE observations of lines of sight with peculiar ultraviolet extinction
Low resolution IUE data were used to derive UV extinction curves for agroup of stars known to have peculiar extinction parameters from ANSdata. The resulting curves have a wide range of appearances. Althoughthe ratio E(BUMP)/E(B-V) differs by a factor of three in the extremecases, the wavelength of maximum absorption does not appear to change.No evidence for new fine structure in UV extinction was found. Thestructure near 62 micrometers in the existing mean extinction curvesappears to be the result of luminosity mismatch errors. The newextinction curves have shapes that separate into two distinct classes;those associated with clear field extinction and those associated withextinction in dense nebular environments. The range of variation in thecurves is so large, the common practice of ironing out the bump canproduce enormous errors in the resultant UV energy distributions whenE(B-V) 0.3.
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Observation and Astrometry data
| Constellation: | Orion |
| Right ascension: | 06h09m00.31s |
| Declination: | +20°38'25.9" |
| Apparent magnitude: | 10.773 |
| Proper motion RA: | 1.3 |
| Proper motion Dec: | -2.9 |
| B-T magnitude: | 11.302 |
| V-T magnitude: | 10.817 |
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