Near-infrared study of the stellar population of Sh2-152

Abstract

Context. The discovery of new massive star clusters and massive stellar populations in previously known clusters in our Galaxy by means of infrared studies has changed our view of the Milky Way from an inactive to an active star-forming machine. Within this scenario, we present a near-infrared spectrophotometric study of the stellar content of the compact HII region Sh2-152. Aims. We aim to determine the distance, extinction, age, and mass of Sh2-152, using for the first time near-infrared stellar classification for several sources in the region. Methods. Using our near-infrared (J, H, and K S ) photometry and the colour-magnitude diagram for the cluster field, we selected 13 bright stars, candidate members of the reddened cluster's main sequence, for H-and K-spectroscopy and spectral classification. This near-infrared information was complemented with an optical spectrum of the ionizing central star to confirm its spectral nature. Results. From the 13 spectroscopically observed stars, 5 were classified as B-type, 3 as G-type, 2 were young stellar objects (YSOs), and 3 remained unclassified (because of the poor data quality). The cluster's extinction varies from A K S = 0.5 to 2.6 mag (A V = 4.5 to 24 mag) and the distance is estimated to be 3.21 ± 0.21 kpc. The age of the cluster is younger than 9.4 Myr and the lower limit to the total mass of the cluster is (2.45 ± 0.79) × 10 3 M . We compare the number of ionizing photons emitted from the OB-type stars with the Lyman continuum photons derived from the radio observations and conclude that both quantities are consistent for the central region of Sh2-152. In contrast, the main ionizing source of the lower region remains unidentified.

The Planck Cold Clump G108.37-01.06: A Site of Complex Interplay between H ii Regions, Young Clusters, and Filaments

“…The distance for star ids S01 and S02 are estimated to be 3600 ± 330 and 3590 ± 250 pc, respectively. Our estimated spectral classifications and distances for S01 and S02 agree well with the published values of S152-S153 H ii regions in the literature (Ramírez Alegría et al 2011), which are likely part of the same cloud in which the S149-S148 H ii regions are associated (see Section 2 and also Tatematsu et al 1985, for details). Considering their distances, S04 and S05 seem to be foreground stars.…”

Masgomas-4: Physical characterization of a double-core obscured cluster with a massive and very young stellar population

“…Spectral classification for Masgomas-4 has followed a similar procedure to that in previous group works (G61.48+0.09 Marín-Franch et al 2009;Sh2-152, NGC 7538 Puga et al 2010;Ramírez Alegría et al 2011;and Masgomas-1, Ramírez Alegría et al 2012). The classification scheme is based on the detection of absorption lines and the comparison of their depth and shape with similar resolution spectra of known spectral types.…”

Discovery of a young and massive stellar cluster

“…To obtain the luminosity and mass functions for both fields, we followed the same procedure as described by Ramírez Alegría et al (2011). First, we projected every star following the reddening vector to the dwarf star sequence, located at our estimated distance, and defined by the magnitudes and colours of Cox (2000).…”

“…To measure OB-type and supergiant stars proper motions, we followed a similar procedure as described by Peña Ramírez et al (2011). We used the 2MASS image as the first epoch and the LIRIS image as the second epoch, with a time baseline of 10.88 years.…”