V442 And outburst - one month after

Since I have my backyard observatory, two years ago, I have acquired around 200 spectra of Be stars. In 2016 I discovered an outburst on QR Vul and the night of august 21st this year, I took a spectrum of V442 Andromedae and found an emission on top of the Halpha absorption line. This was a change compared to the previous spectrum in BeSS database taken end of july during the OHP spectroscopy workshop by Valérie Desnoux (fig. 1).

Fig.1: comparison august 22nd and july 31st spectra

The alert was quickly given to the BeSS community through the ARAS discussion group and the ARAS forum. The ideal observing period on ARASBeAm, a web site used by Be star amateur spectroscopists, has been lowered from 30 days to 1 day for this outburst period. As a side note, this shows the importance of always comparing the spectra acquired with the last one on BeSS database or ARASBeAm website.

The first 30 nights, 95 spectra have been acquired and archived in BeSS database by 8 observers (table 1).

Observer	Spectrograph	#Spectra
Olivier Thizy	echelle	41
Dong Li	Littrow	33
Juan Guarro Flo	echelle	12
Christian Buil	echelle	3
Olivier Garde	echelle	2
Patrick Fosanelli	Littrow	2
Valérie Desnoux	Littrow	1
Jean-Noël Terry	Littrow	1

Table 1: list of observers

Noël Richardson from University of Toledo in Canada, contacted me after the outburst announcement. His initial comments were encouraging "this seems like a rare opportunity to trace the mechanisms of how small ejections in Be stars operate to build a disk. Please keep observing!". He made some spectro-polarimetry observations of his own with a 1m telescope.

V442 And star was long considered as a B star. Bozic & Harmanec (1998) studied its photometric variations and even predicted – a first for this type of stars – a spectroscopic variation with a 430 days period. McCollum et al. (2000) reported the first emission detection on Halpha, classifying this star as part of the Be stars group.

Slechta & Skoda (2004) studied an outburst through early to august 2003 and a new outburst that started in october of the same year. Using He I 6678 absorption line, they found the star rotation period of 2,615 days

Bozic & Harmanec (2004) gave a complete status of the knowledge of this star back then. They suspected a 24-29 period and a longuer one of 630 days (instead of 430 days) for the outbursts. They determined the star characteristics: 17000K effective temperature, 5 solar masses, 11 solar radius. Rotational speed of the star is close to the break out velocity and the star inclination is around 19°, close to pole-on view.

Based on spectra archived in BeSS, Fig. 2 is showing the known state of the Halpha spectral line over the past 15 years. It seems to indicate that outburst last for 3 to 6 months with quiescence phase lasting 6 to around 21 months.

 Fig. 2: V442 And known status over the past 15 years

Fig. 3 shows the evolution of the Halpha line since the outburst discovery, one spectrum selected per day. At the beginning the V (Violet) and R (Red) peaks seem to swing back and forth but then stabilize between september 2nd and 6. Another variable phase occured between september 7th and 10th with smaller variation between 11th and 15th.

Fig. 3: daily evolution of V442 And Halpha line

Coralie Neiner, from Paris-Meudon observatory, kindly suggested to measure the intensity of the two peaks and to trace V/R and V+R over time. Each spectrum has been scaled to 1 on [6580;6590] Angstroems and a gaussian has been fit on [6558;6561] for the V peak and on [6561;6564] for the R peak. Intensity is defined as the difference between the maximum of the gaussian fit and 0.9 where the absorption level has been estimated.

Fig. 4: V/R variations after outburst discovery
(note a very good time coverage on day 29-30 with Dong Li & I)

V/R graph (Fig. 4) shows a high variability for about 11 days, then stabilizes for 6 days, variable again for 5 days, then smaller variations. Same V/R variation folded over the stellar rotation period of 2,615 days shows a fairly good fit (Fig. 5).

It seems that the material initially ejected remained close to the photosphere before moving away and a second ejection occured then.

Noël Richardson wrote some kind & encouraging comments for the team: "The quick V/R changes seem consistent with a blob ejected from the star and in orbit just above the stellar surface. This should make a very interesting project. Many thanks to you for arranging the spectroscopy and to all of the observers for their time, dedication, and enthusiasm."

Fig. 5: V/R variations folded over 2.615 days period

V+R, on the other side, shows a slower variation (Fig. 6) indicating that the V/R variation above are mainly due to non homogeneous material around the star.

Fig. 6: V+R evolutions after outburst discovery

As a conclusion, this study first highlights the interest of long term Be star spectra monitoring and the importance of BeSS database. When observers focus on an outburst in a coordinated way, there are some good quality data collected – thus the importance of ARAS group. In the particular case of V442 And, profession astronomer encouragements and kind comments helped keeping the motivation of the team for coutinuous observations.

As for the results themselves, those are preliminary and additional observations should give us more information on the potentially multiple ejections of small blob of material from this Be star star and how it moves into a keplerian disk.

It is clearly a fun projects and I hope more observers joined the team as the target will still be visible for several months now.

References:

ARAS BeAm: http://arasbeam.free.fr/

ARAS discussion group: https://groups.yahoo.com/neo/groups/spectro-l/info

ARAS forum: http://www.spectro-aras.com/forum/viewtopic.php?f=5&t=1835

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Bozic H, Harmanec P; "HD6226: a new bright B variable with occasional brightenings. Is it an unrecognized Be star?" A&A 330, p222 (1998)

Bozic H, Harmanec P, et al.; "Properties and nature of Be stars , XXII. Long-term light and spectral variations of the new bright Be star HD 6226"; A&A 416, p669 (2004)

McCollum, B. et al.; "First Detection of Hα Emission in the Bright, Variable B Star HD 6226"; American Astronomical Society, 197th AAS Meeting (2000)

Neiner, C. et al.; "The Be star spectra (BeSS) database", AJ p142 (2011)

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Slechta, M., Skoda P., "an outburst detected in the spectrum of HD6226", ASS 296, p179 (2005)