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A new outburst of the yellow hypergiant star Rho Cas

Michaela Kraus, Indrek Kolka, Anna Aret, Dieter H. Nickeler, Grigoris Maravelias, Tõnis Eenmäe, Alex Lobel, Valentina G. Klochkova

Yellow hypergiants are evolved massive stars that were suggested to be in post-red supergiant stage. Post-red supergiants that evolve back to the blue, hot side of the Hertzsprung-Russell diagram can intersect a temperature domain in which their atmospheres become unstable against pulsations (the Yellow Void or Yellow Wall), and the stars can experience outbursts with short, but violent mass eruptions. The yellow hypergiant Rho Cas is famous for its historical and recent outbursts, during which the star develops a cool, optically thick wind with a very brief but high mass-loss rate, causing a sudden drop in the light curve. Here we report on a new outburst of Rho Cas which occurred in 2013, accompanied by a temperature decrease of ~3000 K and a brightness drop of 0.6 mag. During the outburst TiO bands appear, together with many low excitation metallic atmospheric lines characteristic for a later spectral type. With this new outburst, it appears that the time interval between individual events decreases, which might indicate that Rho Cas is preparing for a major eruption that could help the star to pass through the Yellow Void. We also analysed the emission features that appear during phases of maximum brightness and find that they vary synchronous with the emission in the prominent [CaII] lines. We conclude that the occasionally detected emission in the spectra of Rho Cas, as well as certain asymmetries seen in the absorption lines of low to medium-excitation potential, are circumstellar in nature, and we discuss the possible origin of this material.

arXiv.org: 1812.03065

Victor Buso is a really very lucky man! On September 20, 2016 we wanted to test his new camera mounted on a 40-cm Newtonian telescope. He pointed to the spiral galaxy NGC 613 because it was at that time located near the zenith. He took a series of 20s exposures spanning approximately an hour and a half. During the first part (about 40 exposures) there was no sign of anything unusual. After a break of 45 min though the exposures that he took revealed the rise of a supernova (SN 2016gkg). He is the first person to ever achieve that, ie. to capture the rise of a supernova just before its maximum light!

These observations are an unprecedented set of data for supernova physics. According to the recent paper by Bersten et al (incl. Buso) 2018 the data shows the clear presence of the shock breakout phase in the optical, i.e. the phase associated with the propagation of the radiation shock inside the star and its dissolution at the surface (Waxman & Katz 2016). This lasts seconds to a fraction of an hour typically, unless there is enough circumstellar mater ejected from the progenitor star before the supernova explosion then this phase may extend to days. The phase produces bright X-ray/UV flash but its optical manifestation has not been observed. So these observations show that the optical light curve is characterized by an extremely rapid brightening at relatively low luminosity.

What I find very critical in this work is actually how quick-witted Buso was. He is an amateur astronomer that didn’t just take the images. Instead he properly reduced them and he noticed the difference. The next important step was to communicate this to the appropriate channels that allowed for follow-up observations to be obtained in in less than a day later (including Swift X-ray, UV and optical telescopes, see Bersten et al 2018 for a list).

References
Bersten et al, 2018, Nature, 554, 497 (NASA/ADS link)
Waxman & Katz, 2016, arXiv:1607.01293 (arXiv link)

The need for Professional-Amateur collaborations in studies of Jupiter and Saturn

Emmanuel Kardasis, John H. Rogers, Glenn Orton, Marc Delcroix, Apostolos Christou, Mike Foulkes, Padma Yanamandra-Fisher, Michel Jacquesson, Grigoris Maravelias

The observation of gaseous giant planets is of high scientific interest. Although they have been the targets of several spacecraft missions, there still remains a need for continuous ground-based observations. As their atmospheres present fast dynamic environments on various time scales, the availability of time at professional telescopes is neither uniform nor of sufficient duration to assess temporal changes. However, numerous amateurs with small telescopes (of 15-40 cm) and modern hardware and software equipment can monitor these changes daily (within the 360-900nm range). Amateurs are able to trace the structure and the evolution of atmospheric features, such as major planetary-scale disturbances, vortices, and storms. Their observations provide a continuous record and it is not uncommon to trigger professional observations in cases of important events, such as sudden onset of global changes, storms and celestial impacts. For example, the continuous amateur monitoring has led to the discovery of fireballs in Jupiter’s atmosphere, providing information not only on Jupiter’s gravitational influence but also on the properties and populations of the impactors. Photometric monitoring of stellar occultations by the planets can reveal spatial/temporal variability in their atmospheric structure. Therefore, co-ordination and communication between professionals and amateurs is important. We present examples of such collaborations that: (i) engage systematic multi-wavelength observations and databases, (ii) examine the variability of cloud features over timescales from days to decades, (iii) provide, by ground-based professional and amateur observations, the necessary spatial and temporal resolution of features that will be studied by the interplanetary mission Juno, (iv) investigate video observations of Jupiter to identify impacts of small objects, (v) carry out stellar-occultation campaigns.

arXiv:1503.07878

The 4th Panhellenic Meeting of Amateur Astronomers took place in a magnificent area, at the mountain refugee of the Mountaineering Club of Sparta at Mt. Parnonas. The place is located at ~1400m with a huge field working as the best place to park cars and set up all the necessary equipment. Moreover, the area around is full of trees and a fantastic place for camping. More or less 415 people gathered, more than 100 telescopes, 3 nigths of clear unobstructed dark skies, 6 observational workshops (participating in 2 of them: variable star observations and optical observation methodology of meteors) and some talks, and other activities (great for MTB!!) were enough to satisfy even the most demanding person. The organizing commitee did a great jod and managed to fulfill all the needs (both astrononomical and personal).

More available only in greek but no need of language to see photos.