Star formation towards the southern cometary H ii region IRAS 17256−3631

Abstract

IRAS 17256-3631 is a southern Galactic massive star forming region located at a distance of 2 kpc. In this paper, we present a multiwavelength investigation of the embedded cluster, the H II region, as well as the parent cloud. Radio images at 325, 610 and 1372 MHz were obtained using GMRT, India while the near-infrared imaging and spectroscopy were carried out using UKIRT and Mt. Abu Infrared Telescope, India. The near-infrared K-band image reveals the presence of a partially embedded infrared cluster. The spectral features of the brightest star in the cluster, IRS-1, spectroscopically agrees with a late O or early B star and could be the driving source of this region. Filamentary H 2 emission detected towards the outer envelope indicates presence of highly excited gas. The parent cloud is investigated at far-infrared to millimeter wavelengths and eighteen dust clumps have been identified. The spectral energy distributions (SEDs) of these clumps have been fitted as modified blackbodies and the best-fit peak temperatures are found to range from 14 − 33 K, while the column densities vary from 0.7 − 8.5 × 10 22 cm −2 . The radio maps show a cometary morphology for the distribution of ionised gas that is density bounded towards the north-west and ionization bounded towards the south-east. This morphology is better explained with the champagne flow model as compared to the bow shock model. Using observations at near, mid and farinfrared, submillimeter and radio wavelengths, we examine the evolutionary stages of various clumps.

The physical and chemical structure of Sagittarius B2

“…Although the RRL line width cannot be directly used to determine the shock speed, we note that it is significantly larger than the typical expansion velocity of an HII region (10 km s −1 Draine 2011), which points to an additional mechanism of acceleration. One possible origin of the high velocity is the presence of a stellar wind driven by the O 7 star that likely ionizes the HII region (see e.g., Veena et al 2016;Pereira et al 2016;Kiminki et al 2017). We note that velocities of about 35 km s −1 are in agreement with what is obtained by simulations of HII regions of O and B stars driving strong stellar winds (Steggles et al 2017).…”

“…This result raises the question whether other HII regions may also show non-thermal emission. A handful of HII regions have been reported to have negative spectral indices suggestive of a non-thermal component (e.g., Garay et al 1996;Veena et al 2016Veena et al , 2019, indicating that the presence of non-thermal emission in HII regions may be a more common event than previously thought. The advent of extremely sensitive facilities at radio wavelengths such as SKA (Square Kilometer Array) or the ngVLA (next generation Very Large Array) may trigger the systematic search for HII regions with non-thermal emission, thus allowing a study of the conditions under which non-thermal emission exists.…”

“…The HII region AA appears to have pure thermal emission in the center, with a possible contribution of non-thermal emission in the outskirts. The presence of non-thermal emission in the outskirts of HII regions have been found in a handful of objects (e.g., Garay et al 1996;Mücke et al 2002;Veena et al 2016Veena et al , 2019.…”

Radio and infrared study of southern H II regions G346.056−0.021 and G346.077−0.056

“…However, the values obtained from the integrated flux densities are indicative of non-thermal emission (Rosero et al 2016;Kobulnicky & Johnson 1999;Rodriguez et al 1993). Thus a scenario of co-existing free-free and non-thermal emission can be visualized for the H II regions as has been addressed by several authors (Russeil et al 2016;Veena et al 2016;Nandakumar et al 2016;Mücke et al 2002;Das et al 2017). The above interpretation should be taken with caution because GMRT is not a scaled array between the observed frequencies and the observed visibilities span different uv ranges.…”

Radiación no térmica asociada a estrellas de gran masa

“…En otros sistemas que guardan similitudes con las burbujas estelares sí se han encontrado indicios claros de aceleración de CRs, como en los cúmulos compactos de estrellas masivas [8], las binarias masivas con colisión de vientos [64,65], los RSN (por ej., [66]), jets protoestelares [67,68] e incluso quizás en la interacción entre el viento de WR 20b y la cáscara del cúmulo Westerlund 2 [69]. También se ha detectado la presencia de emisión NT en regiones HII [70,71].…”