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Photometric and Spectroscopic Study of Stars in the Field of the Young Open Cluster Roslund 4
We present photometric and spectroscopic observations performed in thefield of the Galactic open cluster Roslund 4, which contains the twocataloged nebulae IC 4954 and IC 4955. UBVRI photometry was carried outin a field of 11'×6' around the clustercenter. Medium-resolution optical spectroscopy has been obtained for 41stars, including previously selected main-sequence and pre-main-sequencecandidate cluster members. Narrowband Hα, [S II], and continuumimages have been secured. The observations allow us the measurement ofdifferent physical parameters for the cluster. Assuming an absorptioncoefficient AV/E(B-V)=3.1 and a reddening slopeE(U-B)/E(B-V)=0.72, we obtain a color excess E(B-V)=1.1+/-0.2 and adistance modulus DM0=11.7+/-0.5. Fitting of isochrones to thecolor-magnitude diagrams gives logage(yr)=7.2+/-0.2, and thespectroscopic measurements provide the value VR=-15.7+/-5.2km s-1 for the heliocentric radial velocity. Among the 41stars with spectroscopic data, 11 stars are probable cluster members onthe basis of their radial velocity, and another 10 are considered aspossible members. Two probable member stars of spectral types A5 and G1show hints of absorption in the Li I 6708 Å line, with respectiveequivalent widths of 0.10 and 0.28 Å, and 22 stars of spectraltypes from B2 to G0 show different degrees of emission in Hα, [NII], and [S II] lines. With the exception of three stars of spectraltype earlier than A0, the emission of which is mainly photospheric, allother emissions seen in Hα and forbidden lines have a nebularorigin. They arise in an ionized cloud that surrounds the cluster and iscausing diffuse emission and, possibly, local variations in theextinction law from star to star. In addition to the stars, spectra ofseveral nebular condensations with relatively higher excitation havebeen analyzed. Two of them have been suggested to be Herbig-Haro (HH)objects. Our spectra indicate that only one of these condensations couldbe considered as an HH object.
| The association of IRAS sources and 12CO emission in the outer Galaxy
We have revisited the question of the association of CO emission withIRAS sources in the outer Galaxy using data from the FCRAO Outer GalaxySurvey (OGS). The availability of a large-scale high-resolution COsurvey allows us to approach the question of IRAS-CO associations from anew direction - namely we examined all of the IRAS sources within theOGS region for associated molecular material. By investigating theassociation of molecular material with random lines of sight in the OGSregion we were able to construct a quantitative means to judge thelikelihood that any given IRAS-CO association is valid and todisentangle multiple emission components along the line of sight. Thepaper presents a list of all of the IRAS-CO associations in the OGSregion. We show that, within the OGS region, there is a significantincrease ( ~ 22%) in the number of probable star forming regions overprevious targeted CO surveys towards IRAS sources. As a demonstration ofthe utility of the IRAS-CO association table we present the results ofthree brief studies on candidate zone-of-avoidance galaxies with IRAScounterparts, far outer Galaxy CO clouds, and very bright CO clouds withno associated IRAS sources. We find that ~ 25% of such candidate ZOAGsare Galactic objects. We have discovered two new far outer Galaxystar-forming regions, and have discovered six bright molecular cloudsthat we believe are ideal targets for the investigation of the earlieststages of sequential star formation around HII regions. Finally, thispaper provides readers with the necessary data to compare othercatalogued data sets with the OGS data.Tables 1, 2 and A1 are only available in electronic form at the CDS viaanonymous ftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/1083
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