Hα Interferometric Optical and Near Infrared Photometric Studies of Star Forming Regions - Part One - the Cepheus-B / SH:2-155 / CEPHEUS-OB3 Association Complex

Details Hα Interferometric Optical and Near Infrared Photometric Studies of Star Forming Regions - Part One - the Cepheus-B / SH:2-155 / CEPHEUS-OB3 Association Complex Hα Interferometric Optical and Near Infrared Photometric Studies of Star Forming Regions - Part One - the Cepheus-B / SH:2-155 / CEPHEUS-OB3 Association Complex

Jun 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...273..619m&link_type=abstract

Astronomy and Astrophysics, Vol.273, NO. 2/JUNII, P. 619, 1993

Astronomy and Astrophysics

Astrophysics

29

H Ii Region Sh2-155, Cepheus B Molecular Cloud, Ir Photometry Of Cepheus Ob3 Association, Premain Sequence Stars And Near Ir Sources

Scientific paper

Here we report the results of a near IR photo- metric study of about 40 stars of the Cepheus OB3 association (subpopulations a and b), of an attempt to detect near IR counterparts of the discrete radio continuum sources reported by Felli et al. (1978), and of the nature of the IR source AFGL 3000. We also give the results of a Hα interferometric, photographic, and CCD imagery study of the Sh2-155/Cepheus B region. Our NIR photometry of the bright members of the association combined with published optical spectroscopy and photometry, yields for the Cepheus OB association the following: (AV)a=2.1 and (AV)b=2.9, AV/E(B-V )=3.0±0.1 and (5log r+5)a+b =9.65±0.15 (or 850±60pc). The O7n star HD 217086 (=BHJ 41) has near infrared excess due to free-free emission from a dense stellar wind. HD 217061 (= BHJ 40) is extended in the near IR (resolution =5'.5), and is responsible for the bright arc seen eastward from it on a [S II] photographic image of the region, and which is ridge B of Felli et al. (1978). From [2.2 μm] scanning of a substantial portion of the Cepheus B molecular cloud and proximity we find 50 low brightness NIR sources. In particular, about 60% of the sources were located in Cepheus B or its immediacy, suggesting that low mass star formation is taking place at a high rate within its boundaries. Except for AFGL 3000, located on the intensity maximum of ridge A of radio source S155A, no bright NIR sources were found at the locations of the discrete 0.610 GHz radio sources 9, 14 and 21 of Felli et al. (1978). The IR source AFGL 3000 is extended, probably excited by a B0(V) star, reddened by 11m.6 in the visual. The NIR, sources 1 and 2 found here are probably young stars of spectral types B6.5(V) and B1.5(V), reddened by 4m.2 and 6m.2 in the visual, respectively. We find for the cloud that the average NIR stellar column density is ρ(NIR) ≥ 12 pc-2. From Fabry-Perot Hoc interferometry of Sh2-155, we find for its radial velocity νlsr = - 15.3±0.4 km s-1 (or dkin = 1.5±0.2 kpc), and a radial velocity gradient in the declination direction of -5.8 km s-1 (or -2.1 km s-1 pc-1). From published CO observations we find the gas content of the cloud to be about 600Msun, a too low of a value to keep the cloud bounded if the velocity gradient is due to rotation. Our BVRI-Hα CCD imagery of the bright Hα knot revealed a low mass pre-main sequence star association embedded in it, and where a high stellar column density ρcol > 220 pc-2 was estimated. From the (I, V-I) and from the (αR,I) diagrams we conclude that at least 50% of the stars in the association can have Hα in emission and are more luminous than main sequence stars, and hence should be T Tauri like objects. The age of the association is estimated to be of about 105 yr. From a crude balance of forces of Cepheus B we discuss its stability. We also revise the cloud models by Felli et al. (1978) and by Panagia & Thum (1981).

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