dimanche 24 septembre 2017

Several records beaten at Observatory of Belle Etoile

The past few weeks have been very busy at the Observatory of Belle Etoile, with lot of observing hours! And several records have fallen in my history of astronomical observations and spectroscopy.


First, during this third quarter (not finished yet) from july to september, I have observed 34 nights for a total of 210 hours. This is my all-time record - and I am recording my observing time for more than 23 years now!

Second, I reached 1334 spectra (58 in Halpha) waiting for validation - well, this is not critical but I kept the BeSS administrators busy! All have been validated now.



Third, including those spectra to be validated, I just passed a key milestone for Be stars with more than 10000 spectra in BeSS. Just few days after Olivier Garde ("sans rancune", Olivier!) crossed this milestone as well... :-)


Fourth, I have acquired more than 500 spectra in Halpha alone, making me entering in the Top 10 of Halpha observers - a first for me.


Fifth, my observing time since I have the observatory crossed the 500 hours observing time milestone. 54% of that time is actually acquiring spectra. My best efficient night was the night of september 19th with an efficiency ratio of 87% ("observatory open time" actually acquiring spectra).

Sixth, I reached one millions seconds of total exposure time since I have the observatory in the backyard.

seventh, and this is a real improvement for me, I reached three night in a raw observing remotely from home. But I still have sometimes the Atik 460 frezing at the end of an exposure, usually right after the first Thorium-Argon calibration or the first acquisition after calibration is done. It freezes after download and image is not saved; I have to physically remove and reconnect the USB cable to make it work again.I suspect a USB issue but haven't found the problem yet.
Otherwise, my only operations at the observatory are to connect the Atik Titan USB, remove telescope cover & add the anti-dew cover, power ON the Atik 460 camera and the mount at the begining & just the reverse steps at the end. Everything else is done remotely through TeamViewer (including file transfer at the end) and it works great.
An important thing is that I have done a pointing model for the Losmandy Titan mount with about 7-8 stars few weeks ago. Since then, the target is always in the guiding chip for GoTo within 40° and otherwise not very far. Pointing procedure has become very easy. I always point on the same side of the pier so that helps. But still, this is a real improvement on my setup!
Anyway, while I still have some motor lags and need to re-adjust the DEC axis (I think it is too tight), the overall the setup works very well now and I have been able to take long sleep while acquiring long series of V442 And spectra for exemple.

watching Star Trek doculmentary during remote observation session

Spectroscopy of Be stars & remote observations rock!

jeudi 21 septembre 2017

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:


Bertaud C, Floquet M; "Observations spectrographiques d'etoiles A a spectre particulier et a raies metalliques"; Journal des Observateurs, Vol. 50, p. 425 (1967)

Bidelman W; "spectral types of 80 early-type stars of variable radial velocity"; PASP 100, p828 (1988)

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)

Sigut T., Patel P.; "the correlation between Halpha emission and visual magnitude during long term variations in classical Be stars"; ApJ 765 p41 (2013)

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

mardi 12 septembre 2017

PC for the observatory

Few months ago, I changed my PC at the observatory. I run with it all my equipment including the weather station - so the PC stays up and running all the time.

As several have asked me about the model & configuration, here are some details.


The PC is a JetWay JBC375:

http://www.mini-itx.com/store/?c=100#JBC375
 

Here is the detail of my order:



Note that I initially received it with only 2GB RAM and I found it was sometimes slow with PRISM v10; with 4GB RAM it runs much smoother!

The hard drive is large for my need but I do not have to remove my old files/acquisition too often so it is convenient.

The computer comes with 4 serial ports (make sure to ask for it), it is important so I could get rid of the USB-to-Serial converter which are not very reliable.


Computer with cover on

Inside the computer (with old 2GB RAM)

Inside the computer

PC serial number


mardi 29 août 2017

Amateur Ring for Astronomical Spectroscopy

ARAS is the Amateur Ring for Astronomical Spectroscopy. I is an informal group of spectroscopists, initiated after 2003 astrophysics scholl in Oléron, France, organized by the french research CNRS. Because it was widely open to amateur astronomers, this is considered as a major pro/am meeting that basically kicked off spectroscopy.

One of the project initiated after Oleron pro/am meeting is the long term monitoring of Be stars, project led by Coralie Neiner from Paris-Meudon observatory. It led to several initiatives such as:
-creation of a web page to present potential pro/am project: ARAS main web page
-creation of a Yahoo discussion group Spectro-L to exchange about pro/am projects in spectroscopy
-kick off of the Be Star Spectra database and Be stars long term monitoring
-design and first batch through AUDE association of the Lhires III spectrograph (leading the creation of Shelyak Instrument company)
-later on creation of ARAS forum
-and ARAS database for non Be star programs (VV Cep stars, P Cygni, cataclysmic variables...)

Professional astronomers have access to equipment we, amateur astronomers, do not have access to: very large telescopes (2m to 10m class), very high resolution spectrographs (HARPS, SOPHIE: 70000 to 140000 resolving power), spectropolarimeters (NARVAL, ESPADON), interferometers, infrared spectrographs, etc...
But they usually need paperwork and long delay before having telescope time access. Because telescope time is expensive, they can't run long term survey and prefere short term results. They can't get telescope time to observe Deneb for exemple - it is not "serious" enough for the professionals! :-)

Amateur astronomers on the contrary have the advantage of beeing reactive. On nova Del 2013 for exemple, first amateur spectra was done couple of hours after the announcement.
The number of amateur astronomical spectroscopists is increasing and I would estimate the number of spectroscopist in the range of 5000-10000, but the one having a slit (or let say a more "scientifcal" spectrograph) in the range of 500-1000, and the one actually doing pro/am work with their equipment in the range of 50-100.
They are also spread over the globe (well, lot of them are in France and Europe and somehow there could be more amateurs doing pro/am spectroscopy in the US/Canada and Asia). This means that when one can't observe a specific target due to bad weather for exemple, another one may have clearer skies and could observe it.

This advantage led for exemple to more than 70000 spectra taken by amateurs (ok, echelle spectra count several times, one for each order... but hey, this is the same for professional astronomers and their number of spectra is even lower).

A good exemple of networking is on the recent outburst of V442 And. When I discovered the outburst, I uploaded the spectra on BeSS database and sent a private note to the administrators letting them know about it.
The following night, I couldn't observe but Christian Buil picked up on it and took one echelle spectrum. Then I observed several nights but on august 27th, my weather was bad and I couldn't observed. I sent a note to Joan Guarro Flo who was able to take one echelle spectrum.
This led to having at least one spectrum per night, so a good coverage of the emission line. Of course it would have be reat to have a continuous 24 hours follow up with support of North America and Asian observers; but at least we got a measurement every 24 hours.

Here is the result of the first 8 nights following the outburst discovery:


It does show that the emission is constantly changing. More observations may reveal a periodic behaviour - we will see later.

My point is that ARAS if more than a Ring... it is a Network of observers. It is an informal  community and behing the friendship that can exist (thanks to pro/am meeting every 3 years, OHP spectroscopy workshop every year, and of course my travels around the globe when I was working for Shelyak), this network leads to mutual motivation, support and collaboration.

Astronomy rocks, Spectroscopy rocks, and ARAS rocks !

dimanche 27 août 2017

Status on OBE observations for the last two years

I have done some stats since the obsevatory is up and running (july 2015), here they are.

I have observed 85 times, for a total of 411 hours. A long break occured from october 2016 to july 2017 (Losmandy Titan mount was getting too erratic to use it properly).

During those two years (removing the long break, 1.33 years actually), I have acquired 296 spectra (56% are spectra of Be stars; 18% VV Cep type stars; 8% P Cygni) for a total exposition time of 200 hours.

The telescope is then accumulating photons for spectra approximatly 50% of the total observing time meaning that 50% of time I am either doing other type of observations (I also count as observing time any public outreach activities...), or telescope is pointing, in maintenance, etc... There is obviously room for improvement there...

After the recent refurbishment, even if I still have some tracking issues (but much less) and I still have to watch what is happening, the observing efficiency was clearly on the rise.
For exemple, the night of august 26th which was just after all the adjustment of the mount, I opened the observatory for 9h15min and I acquired a total of 439min on star spectra; this leads to an efficiency ratio of 79% - not bad at all!
Also the night of august 28th was a good one and the efficiency ratio was 78% (340/435) and I can say this is a very good ratio.
The remaining is opening and closing time, data backup, pointing, centering (this can take some time), finding the right exposure time (I take a 10sec expoure and measure the signal to find the propoer exposure time to get good signal without saturating; this also takes some time).



V442 And biography

Today the observatory had a new addition: a new 18V power supply for the Titan mount. I also got a spring load (electronic) so I could adjust wih more care the balance of the mount. I added 100gr on the counter weight arm as telescope is pointing East (my usual observing side).


While observing several Be stars including V442 And, I am reading several article on V442 And (HD6226) for which I discovered an outburst on august 21st and whose emission profile has been changing every day since then...

In 1967, Bertaud and Floquet wrote a spectroscopical observation report on several peculiar A-type star with metallic lines. Based on 29 january 1960 observation, they indicate that the K line is thin and intense; all lines give a B8I spectral type. HD6226 can't be considered as a peculiar A type star.

In 1988 Bidelman studied several stars with variable radial velocities. HD6226 is then classified as a B3III star.

In 1998 Bozic & Harmanec published an article specifically on HD6226. Based on photometry (including Hipparcos data), they suspected HD6226 to be a Be star with similar behaviour as QR Vul (another Be star for which we have found several outbursts during last ten years).
They found a potential period of 481.3 days for HD6226.

In 2000, McCollum et al. reported the first detection of Halpha emission line. Another report from 2003 indicated that the emission was not seen on spectra taken during November and December 2002 but reappeared on spectra taken between January 19 and March 15, 2003.

In 2004, Bozic & Harmanec published again a dedicated (and long) article on HD6226 (Christian Buil being a co-author!). They found a stellar rotation period of 2.61507 days on He 6678 He I and other metallic lines. They also suspected a period of 24-29 days and a long cycle of 630 days with different durations of the individual cycles for strong emission line episodes.
Their physical parameters for HD6226 are: Teff of 17000K, log g of 3.0 [cgs], 5 solar masses, 11 solar radii. The equatorial velocity is estimated at 213 km s-1 (very close to the break-up limit of the Roche model: 240 km s-1) and the inclination at 19° (almost pole-on).
For them, HD 6226 is probably one of the first B stars for which the Be nature was predicted on the basis of the character of its light and colour changes.
They also mentionned that variability on a time scale of hours cannot be excluded completely – especially since the position of the star in the HR diagram is at the edge of the β Cep instability strip. They couldn't find evidence in photometry for variation in less than 0.4 days but some spectra provide some evidence of moving sub-features travelling accross the He I 6678 line profile. They conclude that HD6226 is a line-profile variable.
They noted an important information on the correlation between photometry (variability in the 0.2 mag range) and spectroscopy (peak intensity of Halpha (V+R)/2): "We note that the observed sequence of events is typical of the positive correlation between brightness and emission strength, as defined by Harmanec (1983, 2000) and discussed semi-quantitatively for another Be star, V839 Her =4 Her by Koubsk´y et al. (1997). Our interpretation is the following: The initial formation of the envelope manifests itself as a pseudophotosphere, a region above the stellar photosphere which is optically thick in the continuum. Since we probably observe HD 6226 more pole-on than equator-on (considering its low v sin i – see below), this pseudophotosphere acts to increase the observed radius of the star which naturally leads to brightening of the object and its apparent evolution from the main sequence towards the supergiant sequence in the colour-colour diagram. As the envelope grows, it gradually gets optically thin in the continuum but opaque in the Balmer lines and this leads to the development of Balmer emission lines and a gradual decrease of the brightness of the object to its undisturbed level."
Regarding the double peak, they mentionned: "It is clear that the inclination under which we observe the star must be low. This, of course, raises the question of the presence of a sharp central absorption seen during the emission episode in the Hα emission line. One possible interpretation is to assume that the Be envelope is sufficiently spheroidal to produce absorption effects even above the poles of the star. Another one would be to assume that the narrow absorption comes from a secondary in a putative binary system. It seems clear, however, that it cannot originate in a stellar wind from polar regions of the star since its RV blueshift with respect to the stellar photosphere – if any – is smaller than 5 km s−1."
Their concluded with: "Clearly, HD 6226 is a very interesting Be star which deserves
further intensive study."

In 2013, Sigut & Patel summarized the correlation between photometry and spectroscopy and proposed a model.
"A positive correlation is seen for most Be stars for which the relevant observations are available, and it is characterized by a decrease in the (visual) magnitude of the system with increasing strength of the Balmer Hα emission (such as an increase in its equivalent width in emission).
In a (U − B)
versus (B − V ) color–color diagram, Be stars with a positive correlation change their luminosity class but not their spectral type (Harmanec 1983). Increasing Hα signifies an increasing disk, and it therefore seems natural to expect an increase in the overall brightness of the system, star-plus-disk, as the disk is built."
V442 And fit into this category of positive correlation, with a low inclination (i=19°).
"On the other hand, an inverse correlation, as described by Harmanec (1983), is characterized by an increase in the magnitude of the system with an increase in the strength of the Balmer emission. In the (U − B) versus (B − V ) color–color diagram, Be stars that show an inverse correlation move along the main sequence, changing their spectral type, but not their luminosity class (Harmanec 1983).
Fewer stars are known to exhibit this inverse correlation: 4 Her (B9e; Koubsky et al. 1997), 88 Her (B7pshe; Doazan et al. 1982), V1294 Aql (B0Ve; Horn et al. 1982), and η Cen (B1.5IVne; ˇStefl et al. 1995).
An inverse correlation is thought to occur when a Be star disk is viewed more edge-on (i.e., at higher inclination angle i; Harmanec 1983). The forming disk can then act to reduce the brightness of the system by blocking the light from the stellar disk, while the small projected area of the disk on the sky keeps the disk emission to a minimum. If the critical inclination angle required to observe an inverse correlation is large enough, then inverse correlations will be statistically less likely to be found than positive correlations."


References
Bertaud C, Floquet M; "Observations spectrographiques d'etoiles A a spectre particulier et a raies metalliques"; Journal des Observateurs, Vol. 50, p. 425 (1967)

Bidelman W; "spectral types of 80 early-type stars of variable radial velocity"; PASP 100, p828 (1988)

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)

Sigut T., Patel P.; "the correlation between Halpha emission and visual magnitude during long term variations in classical Be stars"; ApJ 765 p41 (2013)


vendredi 25 août 2017

Be stars spectroscopy - my current status in BeSS database

Classical Be stars are non supergiant B-type stars that exhibit or have exhibit emission lines over the photospheric spectrum. In the visible domain, the first Balmer line to show emission is Halpha, thus the focus of several amateur astronomers in Halpha monitoring.



Introduction
Be stars are hot B-type stars (effective temperature 10000 to 30000K) with luminosity class III to V (ie: non supergiant stars) whose spectrum has shown at least once an emission line – usually hydrogen Balmer line. Sometimes, other emission lines are visible, for exemple neutral helium. Even when the spectrum goes back to “normal”, the star remains in the Be star class.

Some of those stars are variable with periods of several hours to several days. Pulsations have been observerved in some Be stars as well a magnetic field in one case. The phenomena behind those emission are still being actively studied and amateurs such as I contribute actively to the monitoring of those stars.

After an overview of the Be stars, I focus in this article on beta Lyrae – a binary Be star which was studied for two continuous weeks, and review how amateurs can share their spectra with a Be Star Spectra database implemented with professional astronomers.


spectrum of delta Sco (C11, Lhires III, ST7E, 1h exposure)


Historical background
The first spectroscopic observation of Be stars has been done Secchi, shortly after his systematic analysis of stellar classification. The first Be star to be discovered by father Secchi in 1866 was gamma Cas. In its discovery notification, he mentionned that hesaw it at the same position as the absorption line in other stars such as beta Cas. He also mentionned the bright line was similar to the bright lines when you burn magnesium metal. He had to write a follow up article to clarify that the bright line was of similar phenomenon but not at the same place in the spectrum, so it was not magnesium in gamma Cas!

father Pietro Angelo Secchi
(http://www.klima-luft.de/steinicke/ngcic/persons/secchi.htm)


In 1867, father Secchi discovered beta Lyrae. gamma Cas is a typical Be star, the protype for this stellar type. beta Lyrae is a more complex binary system.



Several Be stars spectra around H-alpha
(spectrographe Lhires III, 2400tt/mm, C11/C14)

The first systematic observation program of emission lines was conducted in 1911 by Ralph Curtis at Ann Arbor in the USA. He published his first article in 1916 with gamma Cas spectra. Like Plavec wrote in his introduction to IAU symposium 70, Curtis selected gamma Cas because “analysing simple spectrum will help studying more complex spectra!”.

The study of Be stars really started at the beginning of 20th century with work of Paul Willard Merrill at Mount Wilson observatory, Otto Struve at Yerkes, and Dean B. McLaughlin at Michigan university. McLaughlin and Curtis published a study on bright Be stars such as gamma Cas, beta Lyr, phi Per, psi Per, Pleione, zeta Tau, beta Mon, HR2142...

Merrill did contribute to several domain in stellar spectroscopy but started with Be star studies (Merrill 1913) and continuously published on the subject through his career.

His observation with a prism objective helped discovering hundred of new Be stars which ended in a catalog of Be stars published at Mount Wilson with Cora G. Burwell in 1933, 1943, 1949, and 1950.

In a new publication of his article, Merrill looked at a subset of Be stars ("shell stars"). He published a list in his 1949 catalog. Here is some exemple of shell stars: gamma Cas, phi Per, psi Per, Pleione (28 Tau), zeta Tau, and 48 Lib.
Spectrum of zeta Tau, Lhires III & C11, 50min exposure

Struve demonstrated that Balmer emission lines are mainly visible on O5-O9 and B0-B5 stellar types, and less for B8, B9, and A0…

Merrill suggested in 1933 a large number of Be stars among B stars, around 15%-20%. This has been studied in several articles summarized by Briot & Zorec in 1981. Tomokazu Kogure and Ryuko Hirata studied in 1982 B stars from the "Bright Star Catalog" (Hoffleit 1964). They found 20% Be stars among B2 type, which is the maximum proportion in our galaxy. When you know that a third of stars you see with naked eyes are B stars... this gives you an idea of how many Be stars are brighter than 6th magnitude!


Astrophysical context
Emission lines coming from an equatorial disk is added to the photospheric absorption spectrum. Central B star emits UV (Lyman continuum) and ionizes the disk, which in turn reemits at high wavelength such as visible domain.



Model of a typical Be star (Kogure & Hirata, 1982)

The same Be star can have different spectrum depending how we view the disk.

Exemple of spectra of Be stars based on view angle (Slettebak 1988)



Be stars have usually a high rotational velocity (several hundreds of km/s), but still below the breakup limit. The disk is an decretion disk (material ejected by the star) and not an accretion disk (material falling toward the star) – this is not a disk coming from the star formation. Another mechanism has to be responsible for the matter to be ejected.

Be stars are close to SPB (Slow Pulsating B stars) and beta Cephei (like BW Vul or sigma Sco) pulsating stars in HR diagram. Non Radial Pulsations have been found in Be stars and could explain how the disk is formed (Rivinius et al. 1998). Magnetic field has also been observed in a Be star (Neiner et al. 2003) which could also explain the phenomenon.

Some other parameters could help such as high rotational velocities and presence of a companion (about a third of Be stars are binaries).

Which lines to expect on Be stars? First, hydrogene lines are the most prominient ones: H-alpha 6562.8, H-beta 4861.3, H-gamma 4340.5, H-delta 4101.7, H-epsilon 3970.1. If the star is in a Be phase, there will be emission in H-alpha. Depending on disk density, there will also be H-beta emission, possibly H-gamma. H-delta and H-epsilon are usually not seen in emission.

Neutral helium HeI can be found for exemple at 4009.3, 4026.2, 4143.7, 4387.9, 4437.5, 4471.5, 4713.1, 4921.9, 5875.6, and 6678.2. If the disk is dense, HeI emission will be seen starting from red lines going to the blue domain the denser the disk is.

Other lines can be visible in Be stars: CII (3920, 4267, 4738, 4745, 6578, 6583...), NII (3995, 4630...), OII (4119, 4367, 4415, 4642, 4649, 4662...), MgII (mainly 4481), SiIII (4552, 4568 & 4575 triplet; several lines around 3800; also at 3924, 4338, 4813, 4829 & 5740), SiII (3856, 3863, 4128, 4131, 5041, 5056, 6347, 6371), and sometimes iron FeII lines...


beta Lyrae
beta Lyrae is a variable star discovered by Goodricke in 1794. With a period of 12.9 days, it is the prototype of close eclipse binaries.

The system is made of a B6-B8 primary star which appears more luminous than the B0-B2e companion whose disk covers around 25% of the sky viewed from the Be star. Jet like structures have been observed, perpendicular to the orbit, with very high velocities (around 1000km/s).

In 2005, two missions monitored this binary Be star. Groups were from CALA (Club d'Astronomie de Lyon-Ampère) and SAR (Société Astronomique de Rennes).

There are 7 binary Be stars in the Bright Star Catalog (Henrichs Huib, private communication): eta Ori, beta Lyr, omi And, VV Cep, HD203338, HD39286, and HD50820. I selected beta Lyr despite the comment from Coralie Neiner that this was a very complex system to study...

3D spectral Ha profiles sorted by binary rotation phase

Spectrogram of beta Lyrae (Ha) made from 32 spectra (3h exposure each)
each substracted by average spectrum


We monitored beta Lyrae for 14 continuous days, with 132 spectra obtained. Results obtained showed how difficult it is to interpret such spectra. Next time, we will listen to professional astronomers and study simpler Be stars!



In parallel to our monitoring, another team (Christian Buil et al.) took spectra with a Lhires III of H-alpha but also sodium doublet. This was a coordinated effort between AstroQueyras and Pic du Midi T60 observatories, two structures where amateur astronomers can request mission and access to 24” telescopes. Resolutions were close for both teams.

The sodium doublet clearly shows interstellar sodium, at fixed wavelength, and sodium from the binary system swinging around due to the system rotation.

Lhires III sodium doublet monitoring (C. Buil et al.)


Multiple parameters can be measured on Be stars spectra: Intensity, V/R (when lines are double-peaked), Equivalent Width, etc...

How to measure V/R ratio on a double peak spectrum

We combined in one graph measured V/R data from AstroQueyras CALA/SAR teams (24inch telescope), Christian Buil (Lhires III, 24inch and C11), François Cochard (Lhires III, C8). The graph shows that reasonable sized telescope and spectrographs such as Lhires III and now eShel can provide accurate data compared to larger telescopes and spectrographs.

V/R measures from several sources of beta Lyr (Halpha)

This study, in general, provided a lot of spectra that have not yet all been processed and analysed. It also shows how complex beta Lyrae system is: it is an eclipsing binary with an accretion disk, magnetic field, polar jet structures, mass transfer between the two stars... whose spectra are very complex to analyze and interpret.


A structured Pro/Am collaboration
Following Oleron 2003, the amateur community did structure itself with the Spectro-L discussion group. It is an excellent support for alerts (outburst, special target to follow...) and general discussion about astronomical spectroscopy.

A portal has also been developped: ARAS (Astronomical Ring for Amateur Spectroscopy). It provides link to key pro/am collaboration campaigns.

Another pro/am school took place at La Rochelle in 2006, 2009 and 2012. Then in 2015 it was organized in conjunction with the WETAL (local event from Lyon astronomy club CALA) in Giron.
Spectroscopy is a technic used by more and more amateur astronomers as SAS (Society for Astronomical Science) colloquiums, VdS meeting in Heidelberg (2008) and several other meeting with AAVSO or BAA indicate. Also, spectroscopy practical workshops have been organised at Observatory of Haute Provence in August or July: OHP 2004, 2005, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016 and 2017!

Through 2006-2007, the GEPI team from Paris-Meudon observatory designed and implemented a Be Star Spectra (BeSS) database with help of amateur astronomers (François Cochard, Valérie Desnoux, Christian Buil, Olivier Thizy). This led to a pro/am database, with multilangage access.


We can already mention two key benefits from the BeSS database. First, a FITS format was defined for spectra which allow better exchange of data between amateurs with key data required for spectral analysis. Also, going through the full process has helped dozen of amateurs to finetune their procedure of spectra acquisition, profile extraction and calibration, etc... I strongly encourages anyone in spectroscopy to go through the process of uploading a classical Be star spectrum.


An easier access to BeSS has been developped for amateur: http://arasbeam.free.fr; amateur can easily check which Be stars should be observed tonight based on uploaded spectra and required observation frequency.

ARASBeAm Be star list; red are urgent one to observe

Mid 2009, more than 1500 amateur spectra have been uploaded in the database by more than 20 different users. In 2010, we reached 10000 spectra. Now (august 2017), the database has 133000 spectra, 71000 from amateur astronomers. Current rate is around 14000 spectra per year, mostly amateur (professional astronomers tend to add the spectra by large batch in BeSS).

VisualSpec free software has the ability to query BeSS and download spectra of a Be star for further study and analysis. BeSS is a goldmine of spectra waiting to be downloaded and studied. Some Be stars already have multiple spectra: gamma Cas, zeta Tau, delta Sco... including some Be stars with specific request from professional astronomers (for exemple upsilon Sgr, COROT targets). BeSS is waiting for everyone to take spectra of Be stars and upload the spectra! There are hundred bright Be stars well accessible with backyard telescopes and commercially available spectrographs.

In August 2008, during a spectroscopy workshop at OHP, an outbusrt of QR Vul was discovered by Valérie Desnoux. Now, this star is quieter but a close monitoring would be beneficial.

Another outburst of lambda Eri was also discovered thanks to BeSS and ARASBeAm.



lambda Eri and QR Vul outbursts


There are hundred Be stars within reach of amateur spectrographs. At the beginning, look for bright and easy targets (but still interesting for the professional community!) such as gamma Cas, zeta Tau, delta Sco, beta Lyr... Then look for fainter targets using BeSS and ARASBeAm.



Again, on top of BeSS, a spectro-L discussion group exist for everyone to share their results, request observations or coordinate some campaigns:


Spectroscopy workshop are also organised on a regular basis at Observatoire de Haute Provence. 40-60 people coming from several countries are coming to observe and progress together.


My own observation program of Be stars
150 years after father Secchi discovery, my observing program is primary focused on Be stars (plus VV Cep which is a different "animal" currently in eclipse and some other strange stars such as P Cygni...).

For exemple, I have observed 165 Be stars from july 2015 to august 2017. My stats are overall ok, I have 7412 spectra (8019 if I include the spectra on hold), helped by the echelle spectrograph as each order count for one spectrum (ie: one observation counts for 23 spectra in BeSS). This makes me #4 in the top amateur observers:


On Halpha, I have 418 (447) spectra so I do not make it in the top 10 (need around 60 more star spectra); but this could be a nice goal for me to achieve... :-)


Otherwise, I am glad to have discovered two outbursts so far.

The first one was QR Vul on july 28th, 2016. This star is switching back and forth between quiet period and outbursts.

The last one is V442 And discovered on august 21st, while the previous spectrum dated july 31st from Valérie Desnoux in BeSS didn't show emission (or very very faint one). This star is a nice one with multiple outbursts through the past 10 years and rapid evolution of V/R (Violet/Red peak ratio) in less than 24 hours!


Conclusions

Be stars are great for amateurs: bright, various line profiles, variable over a wide range of periods, of interest for professional studies... Monitoring Be stars over a long period of time should help understanding their outburst mechanisms.

Pro/am collaborations and the BeSS database will also help to perform statistical research on those objects.


Observer group during one of OHP workshop

It is without doubt that this work can be extended to other fields of interest: RR Lyr stars, novae, epsilon Aurigae, VV Cep, etc.. An ARAS database is actually manually managed by François Teyssier and myself:


For exemple VV Cep database, as this system is now entering into eclipse, includes more than 250 spectra with an excellent time coverage through the "first contact".

But other programs do not have the power of ARASBeAm with a clear list of targets for every night, a real plus for the Be star monitoring program.


Aknowledgements
I would like to thank Christian Buil for his continuous and enormous work on spectroscopy among others things. He would like to thank Coralie Neiner and the whole GEPI team for their support. And of course Valérie Desnoux for her great visualSpec software.


Key Links
Liste Spectro-L: http://groups.yahoo.com/group/spectro-l/
ARASBeAm: http://arasbeam.free.fr
BeSS: http://basebe.obspm.fr
Atlas C. Buil: http://astrosurf.com/buil/us/becat.htm


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28 Tau spectrum


Note: This article has been published in similar form in french in SAF Astronomie magazine and also in english during SAS symposium in 2008. He has been also published on Shelyak web site.