Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003aj....126.1861b&link_type=abstract
The Astronomical Journal, Volume 126, Issue 4, pp. 1861-1870.
Astronomy and Astrophysics
Astronomy
7
Ism: H Ii Regions, Ism: Individual (Sh 2-128), Stars: Formation
Scientific paper
Near-infrared imaging photometry supplemented by optical spectroscopy and narrowband imaging of the H II region Sh 2-128 and its environment are presented. This region contains a developed H II region and a neighboring compact H II region associated with a pair of water maser sources. Midway between these, the core of a CO cloud is located. The principal ionizing source of Sh 2-128 is an O7 star close to its center. Slit spectroscopy was used to obtain nebular line fluxes, abundances, and the physical parameters of Sh 2-128. This H II region is optically thin from the optical to the radio and appears to be ionization-bounded. The present JHKs images show the presence of a number of point sources and nebular emission knots with large near-infrared excesses in the northern Sh 2-128N. One of the three red Ks knots coincides with the compact H II region. A few of the infrared-excess objects are close to known mid- and far-infrared emission peaks. Star counts in J and Ks show the presence of a small cluster of B-type stars, mainly associated with Sh 2-128N. Except for the youngest, reddest objects, the stars in the whole region are moderately obscured. The JHKs photometric properties, together with the characteristics of the other objects in the vicinity, suggest that Sh 2-128 and Sh 2-128N constitute a single complex formed from the same molecular cloud but with ages ~106 and less than 3×105 yr, respectively. A new spectroscopic distance of 9.4 kpc is derived. This implies a galactocentric distance of 13.5 kpc and z=550. No molecular hydrogen emission was detected at 2.12 μm from any part of the surveyed region.
Based on observations collected at the Observatorio Astronómico Nacional, San Pedro Mártir, B.C., Mexico.
Bohigas Joaquin
Tapia Mauricio
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