Archive for 2016

Chapter Czechia closes

Posted December 22, 2016 By grigoris

So…these are my final moments in the office that I spend the last 2.5 (almost) years! A lot of memories and experience gained. I am grateful to Michaela Kraus and other colleagues for their hospitality and their interest in my scientific and social life. Nevertheless, a cycle has finished and now I move on.

In about half an hour I will be traveling to Greece for holidays and then to Chile and University of Valparaiso!

Happy holidays!

Almost ready!

Almost ready!

A last (winter) view from the office.

A last (winter) view from the office.

The 2016 Massive Stars meeting in New Zealand

Posted December 1, 2016 By grigoris



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).

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!

Me and

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.

Our most recent work comes as a proceedings paper for the conference “Stars: from collapse to collapse” (Special Astrophysical Observatory, Nizhnij Arkhyz, Karachai-Cherkessian Republic, Russia, 3-7 October 2016):

The yellow hypergiant – B[e] supergiant connection

A. Aret, M. Kraus, I. Kolka, G. Maravelias

B[e] supergiants and yellow hypergiants share a number of common properties regarding their circumstellar environments. Using the forbidden [O I] and [Ca II] lines as disk tracers, we suggest the presence of a Keplerian disk or ring around the yellow hypergiant V509 Cas and confirm the pole-on inner disk around V1302 Aql. These findings indicate a change in mass-loss behavior from spherical in cooler yellow hypergiants to axisymmetric in the hotter ones during the passage through the Yellow Void. The accumulation of material in the equatorial plane reminds of the disks of B[e] supergiants, supporting the suggestion that yellow hypergiants might appear as B[e] supergiants after they reach the blue edge of the yellow instability domain.

arXiv: 1611.06044

The New DUSTER !

Posted November 21, 2016 By grigoris



Workshop on Python and IRAF/PyRAF

Posted November 16, 2016 By grigoris

Between 12 to 19 of September 2016, we organized the Ondřejov Summer School 2016, which was held at the Stellar Stellar Department of the Astronomical Institute (Czech Academy of Sciences), in Ondřejov. The main aim of the school was to provide students hands-on experience with real observational data, i.e. to understand observations, reduce them, and discuss their results. This project-oriented activity was supplemented with lectures on various techniques and one of them was a workshop on Python and IRAF/PyRAF.

As a workshop the main focus was given to show examples that the students could repeat at the own computers. Its structure was based on a very small introductory talk and then examples of how to use Python and IRAF in real problems. With this post I make public all of this material both as a reference and as a (hopeful) help to others.


  • Introductory talk [ .pdf / .odp ]
  • Talk images [ .tar.gz ]
  • Videos – (I need to work on this !)
  • IRAF files (will be added later)

    All of this work is licensed under CC-BY-SA – which means that you can work on it and expand!
    If you like it and want to refer to this work, please cite it as:
    G. Maravelias 2016, “Workshop on Python and IRAF/PyRAF”, Ondřejov Summer School 2016, Ondřejov, Czechia
    online at:

  • How many exoplanets in our Galaxy?

    Posted October 30, 2016 By grigoris

    In Cassan et al. 2012 (Nature, 481, 167), “One or more bound planets per Milky Way star from microlensing observations“) we read the following very interesting statement:

    Here we report a statistical analysis of microlensing data (gathered in 2002–07) that reveals the fraction of bound planets 0.5–10 AU (Sun–Earth distance) from their stars. We find that 17 +6/-9 % of stars host Jupiter-mass planets (0.3–10 MJ , where MJ = 318 M⊕ and M⊕ is Earth’s mass). Cool Neptunes (10–30 M⊕) and super-Earths (5–10 M⊕ ) are even more common: their respective abundances per star are 52 +22/-29 % and 62 +35/-37 %. We conclude that stars are orbited by planets as a rule, rather than the exception.

    LambdaCDM vs. MOND

    Posted October 21, 2016 By grigoris

    Even though the fight between Lambda(Λ)CDM and MOND theories is a confirmed fact, automatic processes (like listing of new arxiv papers) make it more … provocative and/or funny.


    Finally after almost a year, our proceedings paper on the B[e] supergiant LHA 120-S 73 is out! It is based on a poster (2015-58aaa-torres-s73) presented on the 58th Annual Meeting of the Argentinian Astronomical Society (La Plata, Argentina, Sep 14-18, 2015) and connected also with our last refereed paper.

    Exploring the circumstellar disk-like structure of the B[e] supergiant LHA 120-S 73

    Torres A. F., Cidale L., Kraus M., Arias M. L., Maravelias G., Borges Fernandes M., Vallverdú R.

    The Large Magellanic Cloud hosts the peculiar B8-type star LHA 120-S 73. Belonging to the B[e] supergiant group, this star is surrounded by large amounts of material which forms a circumstellar disk-like structure, seen more or less pole-on. Within its dense and cool circumstellar disk, molecules form and dust condensates. Based on medium and high-resolution optical and infrared spectroscopic data, we study the structure, kinematics and physical properties of the disk using different tracers, as the emission lines of [Oi] and [Caii] for the innermost gaseous atomic region and the first-overtone bands of CO for the inner border of the molecular disk. We also analyze near-infrared mid-resolution spectra to search for the presence of other molecules and mid-infrared low-resolution spectroscopic observations to study the composition of the dust component.

    NASA ADS: 2016BAAA…58..120T

    LaTeX tip to comment out large portion of text

    Posted October 10, 2016 By grigoris

    Not very obvious but:


    and some more bla here

    so LaTeX doesn’t compile anything within this if clause.

    [1] TeX.stackexchange- Commenting out large sections, accessed on Oct 10, 2016

    Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73

    M. Kraus, L.S. Cidale, M.L. Arias, G. Maravelias, D.H. Nickeler, A.F. Torres, M. Borges Fernandes, A. Aret, M. Cure, R. Vallverdu, R.H. Barba

    We aim to improve our knowledge on the structure and dynamics of the circumstellar disk of the LMC B[e] supergiant LHA 120-S 73. High-resolution optical and near-IR spectroscopic data were obtained over a period of 16 and 7 years, respectively. The spectra cover the diagnostic emission lines from [CaII] and [OI], as well as the CO bands. These features trace the disk at different distances from the star. We analyzed the kinematics of the individual emission regions by modeling their emission profiles. A low-resolution mid-infrared spectrum was obtained as well, which provides information on the composition of the dusty disk. All diagnostic emission features display double-peaked line profiles, which we interpret as due to Keplerian rotation. We find that LHA 120-S 73 is surrounded by at least four individual rings of material with alternating densities (or by a disk with strongly non-monotonic radial density distribution). Moreover, we find that the molecular ring must have gaps or at least strong density inhomogeneities, or in other words, a clumpy structure. The mid-infrared spectrum displays features of oxygen- and carbon-rich grain species, which indicates a long-lived, stable dusty disk. We cannot confirm the previously reported high value for the stellar rotation velocity. The line profile of HeI 5876 A is strongly variable in both width and shape and resembles of those seen in non-radially pulsating stars. A proper determination of the real underlying stellar rotation velocity is hence not possible. The existence of multiple stable and clumpy rings of alternating density recalls ring structures around planets. Although there is currently insufficient observational evidence, it is tempting to propose a scenario with one (or more) minor bodies or planets revolving around LHA 120-S 73 and stabilizing the ring system, in analogy to the shepherd moons in planetary systems.

    arXiv:1607.00152 | NASA ADS: 2016A&A…593A.112K