Archive for July, 2015

The equivalent of 1 erg

Posted July 28, 2015 By grigoris

A very common unit of energy in Astronomy is erg. There are stellar sources that emit up to 1040 erg/s (or even more for galaxies). But, how could we understand “how much” erg is? An interesting and funny example is given in the Wikipedia [1]:

“An erg is approximately the amount of work done (or energy consumed) by one common house fly performing one “push up”, the leg-bending dip that brings its mouth to the surface on which it stands and back up”

Will you ever forget that ?

[1] Erg, (last visited July 28, 2015) – after ref. 2: Filippenko, Alex, Understanding the Universe (of The Great Courses, on DVD), Lecture 44, time 24:30, The Teaching Company, Chantilly, VA, USA, 2007

June 2015 has been quite busy as I participated in two conferences:

  1. The Physics of Evolved Stars (Nice, France; June 8-12, 2015) – poster contribution

    Title: “Disk tracing for B[e] supergiants in the Magellanic Clouds”

    Abstract: “The B[e] supergiants are an important short-lived transition phase in the life of massive stars, in which enhanced mass-loss leads to a complex circumstellar environment containing atomic, molecular and dust regions of different temperatures and densities. A number of important emission features probe the structure and the kinematics of the circumstellar material. We focus on the [OI] and [CaII] emission lines in comparison to our previous work (Aret et al. 2012), which we further extend by doubling the number of B[e] supergiants studied.”

    In this work we (myself, Michaela Kraus, and Anna Aret) presented our recent results obtained from FEROS observations on Magellanic B[e] Supergiants. We have identified the [CaII] lines in another 4 sources and along with other important disk tracers we show their spectra for the first time. Moreover, for a few number of sources we investigated their spectral variability and some results are under way.

    A couple of photos of our (mine and Anna’s) posters follow:



  2. The 12th Hellenic Astronomical Conference (Thessaloniki, Greece; June 28 – July 2, 2015) – oral contribution

    Title: “Tracing the disks around B[e] supergiants in the Magellanic Clouds”

    Abstract: “Massive stars affect strongly the insterstellar medium through their intense stellar winds, which transfer momentum and energy to the interstellar medium and enrich it with 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. Since these phases are not well-understood and not predicted accurately by theory observations are needed in order to understand the complex circumstellar environment around these stars.
    In particular, B[e] supergiants are often surrounded by rings or disk-like structures, combining atomic, molecular and dust regions of different temperatures and densities. Using high-resolution optical spectra, obtained with the FEROS instrument mounted at the MPG/ESO 2.2m telescope, we examine a number of important emission features which probe the structure and the kinematics of their circumstellar environment. We investigate the [OI] and [CaII] emission lines in comparison to our previous work (Aret et al. 2012), which we further extend by doubling the number of B[e]SG studied in the Magellanic Clouds.”

    Well, even though it is almost the same subject I did have the opportunity to discuss it with a totally different audience. Moreover, we had time to work on some kinematical modelling of the line profiles for which I presented some preliminary results.

    There are no photos to follow (even though I carried my camera and there were so many smart phones!).

Back to (my) school!

Posted July 18, 2015 By grigoris

On Thursday 14th of May 2015 I had the unique opportunity to give a talk about Astronomy at the high school I graduated from in Aigaleo (Athens, Greece). As I have moved away from Aigaleo since 2007 and my visits in Athens are scarce the least, it is difficult to think of such an event (which should account for the other side’s interest too!).

An invitation was sent to the Hellenic Amateur Astronomy Association (HAAA) to ask for the possibility to organize an astronomical event at the 1st high school of Aigaleo. Astronomy was one of the supplementary courses at the high school to be chosen freely by students. However, it is one of the courses discarded recently after major changes in the curriculum. Fortunately, there are still (some) professors who spend extra hours with their students to offer them this opportunity (outside their work schedule and the curriculum of course!). The HAAAA tries to help bridge this gap by providing experienced outreach speakers and telescopes for public observing.

[There is not enough space and actually it is outside of the scope of this post to describe the activities of the Hellenic Amateur Astronomy Association (perhaps I should make one? in the mean time take a look at the poster of Voutyras et al., “10 Years of Developing Outreach Techniques and Best Practice by the Hellenic Amateur Astronomy Association”, European Planetary Science Congress 2013, held 8-13 September in London, UK, but astronomical events for the public and students are routinely organized, always including at least a talk and observation through telescope].

However, due to many other obligations at the time the event was difficult to organize. Moreover, the professor and the students were unwilling to postpone the whole event for later this year, since they had worked on the topic so far and the academic year was reaching its end. As I was planning to visit Crete a few days later (than the initial date they proposed) I though that it would be a great opportunity for me to give this talk! And since I had a connecting flight in Athens perhaps I could change my flight to Crete for the next day and spend more time at the event. After some mail exchanges the school agreed to change the day so it was left to me to decide if I could attend it or not. However, changing the ticket proved to be more expensive than what I had paid already for! In that case another speaker should be found.

But … would I spend 3 hours (doing nothing…) at the airport while the event would took place anyhow at my school? Of course not! So, a radical decision was made: I would ask from a friend to come and get me from the airport, head down to Aigaleo (~40 min by motorbike), spend about an hour there, and return me again at the airport (hopefully) on time to catch the plane for Crete!

Manos Kardasis (a friend with who I have shared many “astronomical adventures”) was the “volunteer” to become the “taxi” motorbike. I arrived at the Athens airport at the 19:45 and he was waiting to pick me up and drive to Aigaleo. Around 20:25 we reached the school. Fortunately, all students were there and after the necessary introductions with the professor we managed to gather all people inside the room within 10 min (probably a record time for such events!), as I could not spend more than an hour there. It was about 20:35 when I started my talk.

Some shots during the presentation

I began by presenting a short bio of myself, not due to any selfish reason, but mainly to show them and stress the fact that I have graduated from the very same school (something they didn’t know beforehand!). That of course raised some cheers by the students. I went on to speak about Astronomy and more specifically about “Massive Stars … and some interested cases”.


It is usual in most public talks of this kind to present more general subjects (like our Solar system). I had decided to speak about what I am currently working on (such as the B[e] supergiants and the High-Mass X-ray Binaries), how they are connected with massive stars, and why the latter are important in our understanding of stellar and galactic evolution. And yes, I did included images that are more appropriate for professional audience (only a few though!). I know that this was too much information to be understood by high school students but, at the time, I though that I could give them just a taste of real scientific aspects (and not just pretty images or graphics). After all, these students do not have often opportunities to listen to and, moreover, to interact with scientists.


I planned for a short talk (~20-30 min) to allow more time for questions and interaction with the students, which was actually the part that I was anticipating. And indeed it was the most interesting with questions ranging from which professors I had when I was in school (obviously we had many in common!), up to Hawking radiation and stellar evolution simulations (!).


The time passed quickly and by 21:30 the telescopes were ready outside, waiting for the students, while we had to ride back to the airport. Even though the bike’s temperature alarm was on, we fortunately managed to get to the airport on time (around 22:10), so I was able to pass security, go to gate and relax a bit before my flight (at 22:55).

Even though it was indeed a very tight plan I really enjoyed it. It was great that I returned back to my school (after 17 years !) to make a presentation on what I am currently working on as an astronomer. Even more important I am pleased by the fact that I was able to give back something to a place that I know well that these opportunities are rare.

I am deeply indebted to Manos Kardasis for his unconditional commitment to help with the materialization of this plan (and for the photos also!), and Manos Vourliotis who organized the event.

NASA’s close look on Pluto (by Peblo)

Posted July 15, 2015 By grigoris

Even though New Horizons has just passed from Pluto and sent us some magnificent images, it didn’t manage to uncover all the details of Pluto.

Luckily, PEBLO give us another great view of Pluto:

Pluto by Peblo