PALOMAR/TRIPLESPEC OBSERVATIONS OFSPITZER/MIPSGAL 24 μm CIRCUMSTELLAR SHELLS: UNVEILING THE NATURES OF THEIR CENTRAL SOURCES

Abstract

We present near-IR spectroscopic observations of the central sources in 17 circumstellar shells from a sample of more than 400 "bubbles" discovered in the Spitzer/MIPSGAL 24 µm survey of the Galactic plane and in the Cygnus-X region. To identify the natures of these shells, we have obtained J, H, and K band spectra with a resolution ∼2600 of the stars at their centers. We observed 14 MIPSGAL bubbles (MBs), WR149, and 2 objects in the Cygnus-X region (WR138a and BD+43 3710), our sample being about 2.5 magnitudes fainter in K band than previous studies of the central sources of MBs. We use spectroscopic diagnostics and spectral libraries of late and early type stars to constrain the natures of our targets. We find five late type giants. The equivalent widths of their CO 2.29 µm features allow us to determine the spectral types of the stars and hence derive extinction along the line of sight, distance, and physical size of the shells. We also find twelve early type stars, in nine MBs and the 3 comparison objects. We find that the subtype inferred from the near-IR for WR138a (WN9h) and WR149 (WN5h) agrees with that derived from optical observations. A careful analysis of the literature and the environment of BD+43 3710 allows us to rule out the carbon star interpretation previously suggested. Our near-IR spectrum suggests that it is a B5 supergiant. At the centers of the nine MBs, we find a WC5-6 star possibly of low-mass, a candidate O5-6 V star, a B0 supergiant, a B/A type giant, and five LBV candidates. We also report the detections of emission lines arising from at least two shells with typical extents (∼ 10 ′′ ) in agreement with those in the mid-IR. We summarize the findings on the natures of the MBs since their discovery, with 30% of them now known. Most MBs with central sources detected in the near-to mid-IR have been identified and are red and blue giants, supergiants, or stars evolving toward these phases including, in particular, a handful of newly discovered Wolf-Rayet stars and a significant number of LBV candidates.

MN48: a new Galactic bona fide luminous blue variable revealed bySpitzerand SALT

“…Searches for compact nebulae using the Spitzer data resulted in discovery of many dozens of compact nebulae, whose geometry is reminiscent of that of the nebulae associated with the already known LBVs (Gvaramadze, Kniazev & Fabrika 2010b;Wachter et al 2010;Mizuno et al 2010). Spectroscopy of central stars of these nebulae showed that many of them have spectra similar to those of the LBVs, which further supports the LBV nature of these stars (Gvaramadze et al 2010a(Gvaramadze et al ,b, 2015aWachter et al 2010Wachter et al , 2011Stringfellow et al 2012a,b;Flagey et al 2014;Kniazev & Gvaramadze 2016). The majority of the compact nebulae discovered with Spitzer were detected in 24 µm images obtained with the Multiband Imaging Photometer for Spitzer (MIPS; Rieke et al 2004) within the framework of the 24 and 70 Micron Survey of the Inner Galactic Disk with MIPS (MIPSGAL; Carey et al 2009) and other Spitzer programmes 1 .…”

High-resolution Very Large Array observations of 18 MIPSGAL bubbles

“…During its evolution the star can therefore appear as spectral type O (Davis et al 2005). The distance calculated by Flagey et al (2014) is however too large to be compatible with this hypothesis. We suggest that the distance may have been over-estimated in the hypothesis of a post-AGB star.…”

“…It is interesting to notice that while for MGE 042.0787+00.5084 and MGE 030.1503+00.1237 the radio is cospatial with the 24-µm emission, this is not the case for MGE 027.3839-00.3031, where the radio nebula seems unrelated to IR. From near-IR spectroscopy, Flagey et al (2014) proposed MGE 042.0787+00.5084 and MGE 030.1503+00.1237 as LBV candidates. Ongoing spectroscopic studies on MGE 027.3839-00.3031 seem to support the same hypothesis (Silva et al submitted).…”

“…The high resolution radio image reveals that it is a compact source approximately 10 × 7 arcsec 2 . Flagey et al (2014) suggested that its central star could be an O5-6V, based on near-IR spectroscopy, but they however warned that this classification is uncertain. They estimate a distance of 11 kpc based on near-IR colours.…”

VLT/SINFONI Observations of Spitzer/MIPSGAL 24 μm Circumstellar Shells: Revealing the Natures of Their Central Sources

“…As of 2014, the year of the most recent paper identifying central sources of MBs, a total of 128 central sources were identified (e.g., Gvaramadze et al 2009Gvaramadze et al , 2010Wachter et al 2010Wachter et al , 2011Mauerhan et al 2011;Flagey et al 2014;Nowak et al 2014). In this paper, we extend the attempt to identify central sources of all MBs with a sample of 55 MBs using observations from the European Southern Observatory (ESO) Very Large Telescope (VLT) located on Cerro Paranal using the Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) (Eisenhauer et al 2003;Bonnet et al 2004).…”