maravelias.info

Auckland

The Massive Stars meeting of 2016 takes place in Auckland, in New Zealand. I was fortunate enough to be given the opportunity to present two works, one poster and one talk during the splinter session on X-rays from massive stars. I have been working hard to finish them, producing the final results almost a day before my presentation. Fortunately, everything went fine and then since Tuesday I am enjoying the conference more relaxed!

1. “The circumstellar environment of B[e] Supergiants” | nzstars2016-poster (pdf)

G. Maravelias, M. Kraus, L. Cidale, M. L. Arias, A. Aret, M. Borges Fernandes

Abstract: Massive stars affect strongly the insterstellar medium through their intense stellar winds and their rich chemically processed material as they evolve. This interaction becomes substantial in short-lived transition phases of massive stars (e.g. B[e] Supergiants, Luminous Blue Variables, Yellow Hypergiants) in which mass-loss is more enhanced and usually eruptive. A complex environment, combining atomic, molecular and dust regions, is formed around these stars. In particular, the circumstellar environment of B[e] Supergiants is not well understood. To address that, we have initiated a campaign to investigate these environments for a sample of Galactic and Magellanic Cloud sources. Using high-resolution optical and near-infrared spectra (using MPG-ESO/FEROS, GEMINI/Phoenix and VLT/CRIRES, respectively), we examine a set of emission features ([OI], [CaII], CO bandheads) to trace their physical conditions and kinematics in their formation regions. We find that the B[e] Supergiants are surrounded by a series of single and/or multiple equatorial rings, of different physical conditions (temperature, density), a probable result of previous mass-loss events. In many cases the CO forms very close to the star, while we notice also an alternate mixing of densities and temperatures (which give rise to the different emission features) along the equatorial plane.

A photo of my poster (not very well illuminated).

2. “Hα imaging for BeXBs in the Small Magellanic Cloud” | nzstars2016-talk (pdf)

G. Maravelias, A. Zezas, V. Antoniou, D. Hatzidimitriou, F. Haberl

High-Mass X-ray Binaries consist of an early-type (OB) massive star and a compact object (neutron star or black hole), which accretes matter from the massive star either through strong stellar winds and/or Roche-lobe overflow in supergiant systems or through an equatorial decretion disk in, non-supergiant, OBe stars (Be X-ray Binaries;BeXBs). Due to these disks the BeXBs display strong Balmer line emission in their optical spectra. At the same time they are among the brightest sources when observed with narrow-band Ηα imaging. The Small Magellanic Cloud (SMC) hosts a large number of BeXBs (almost 100) and offers a unique laboratory to examine these sources with a homogenous and consistent approach. Driven by this, we performed an Hα survey of the SMC (covering both the Bar and the Wing regions) using wide-field cameras (WFI at the MPG/ESO 2m, and MOSAIC at the CTIO/Blanco 4m telescopes). We obtained broad-band R and narrow-band Hα photometry, and identified ~10000 Hα emission sources down to a sensitivity limit of 18.7 mag (equivalent to ∼B8 type Main Sequence stars). We find that OBe stars (the parent population of BeXBs) are 13% of the total OB star population in the SMC down to 18.7 mag, and by investigating this fraction as a function of the brightness of the stars we deduce that Hα excess peaks at spectral range O9-B2. Using the most up-to-date numbers of BeXBs in the SMC we find their fraction with respect to the OBe stars to be in the range ∼ 0.5 − 1.4 × 10^(−3) BeXB/OBe, a direct measurement of the formation rate of BeXBs in the SMC.

Conferences are always a great place to meet old friends and make new ones. The two following photos show exactly that!

The 2016 Ondrejov AsU post-doc Alumni they find each other at the other side of the Earth! From left to right: GM, Anthony Herve, and Mary Oksala [CC-BY-SA-NC].

Meeting my new colleagues at the University of Valparaiso, Chile. From left to right: Ignacio Araya, Catalina Arcos, Alex Gormaz-Matamala, and Michel Cure. Taken from level 51 of Auckland’s Sky Tower, at 186 m high[CC-BY-SA-NC].

UPDATE 22/02/2017: The proceedings paper on “Hα imaging for BeXBs in the Small Magellanic Cloud” has been uploaded at arXiv:1702.04606.