A mission at the Pic du Midi Observatory

The Pic du Midi is a mountain in the pyrenean mountain at the border of France and Spain. The observatory was created in 1878 and offically became a national observatory in 1910. Since then, it produced world-class images from the planets and the sun and now deep sky observation with the largest telescope on the national ground. In 1982, the observatory opened its doors to advanced amateurs with the usage of a 60cm telescope. In 1998, the summit had a big transformation and converted into a popular place for turism but the scientific activities never stopped. In this condition, amateurs can still continue to make missions at the T60, sharing the life of professional Astronomers under a clear sky, at 2870m - When you get there, and enjoyed the charming vision of the milky way, it is hard to come down in the plain... It is our privilege to spend there about 2 weeks in a row, all night and day dedicated to astronomy.

The Pic du Midi site

At the border of Spain and France, the Pic du Midi is one of the highest summit in the pyrenean mountain. Its location just at the beginning of the chain provides excellent condition for quiet atmosphere and thus clear sky. Not far from here, is the Tourmalet pass, famous for the cycling tour "Tour de France" and Gavarny circus.  It is now open for turism, with a museum and unforgettable view on the mountains. Scientific operations are apart and share the place with the turists. Official Observatory website here Turism website here

The T60 "operation"

Amateurs who want to make a mission to the T60 telescope shall apply at the Association T60 - Visit its website at http://astrosurf.com/t60 The T60 is just on the south side of the Pic du Midi buildings, as seen on the pictures

A convention signed with the observatory makes this operation possible. We are assimilated as scientific, have rooms there and take lunch with the observatory people. The T60 telescope is a reflector with a 60cm mirror diameter. It is open at f/3.5. The telescope has digital encoder to accurately point to faint stars and a new system of motorization. In our case, we brought a specific spectrograph to make stars spectra. A T60 mission consists in a specific topic of observation, which can be of interest for the professionals. As for example: comet observations, asteroid occultation, variable star photometry, supernova detection... and of course, spectrography !

Our mission: Spectrography of Corot Be Stars

Christian and I are specialized in spectrography for long time now. I started the Be Star survey in 1992, with very old CCD camera and a cumbersome spectrograph on the T60, in the "old days", at the "old Pic", before renovation for large turism activities. And Christian designed several handy spectrograph for amateurs (also used in universities) and continued the Be Star survey, multiplying by five the "database", from his home location, at Toulouse. Be Stars are hot (20000°K), blue, and rapid rotator stars, spectral type "B". Some of them exhibits emission lines in their spectrum which indicates the presence of a disk of matter around the star. The Be phenomenon is the study of the emission variability and try to understand the mechanism of the matter ejection. In Be, "e" stands for "emission".

We have now established collaboration with a team at Meudon (Paris) observatory on the Be Stars. They gave us a list of Be Stars, quite faint, which are part of the satelilte "Corot" program. Corot will be in operation in Jan 2007. Its mission is the photometric observation (study of brightness) of stars "sismology of stars" and possible detection of exoplanets by the transit method. Corot website It is of interest to take spectra of those stars, in advance, so they can be correlated with the later photometric records. It also means that more missions in the time to come shall happened, with other amateurs, to continue to take spectra during the Corot operation.

Transit method: a planet which orbits around a star can eclipse the star if in the right plane of observation and produce a short decrease of star brightness

The T60 instrument and the observation procedure

The LhiresIII (see description here) is an amateur designed spectrograph. It can ben seen on the picture on the left, mounted to the focal plane of the telescope

It is a slit spectrograph. The tricky part is to keep the star "in the slit". So, we use a video camera with a reflective slit to track on a screen the position of the star during the exposure. With the telescope control command, we adjust the telescope poistion to maintain it. And we do that during the 10 times 5 minutes exposure, (one hour). Then we switch an internal mirror and ligth on a neon lamp to take a reference spectrum of a known gas to later calibrate in wavelength the star spectrum. Every 15 minutes, someone has to move the dome aperture, and assist when pointing the next faint star. During the night, others can go on the terraces and takes sky pictures and we relay each other. Toward 4:00 am, we have the capability and we enjoyed it a lot, to take a short breakfast in the cafeteria, as the camera is taking dark images for later pre-processing.

The results

We are very pleased by the results. One can see here spectra with a good signal to noise ratio, with a R=6500 resolution (sampling is 0.34 angström per pixel) for stars down to mag 10 The benefit of using a 60cm in clear sky is obvious. Those results could not have been obtained by amateurs with their personal instrument. The results are published on the official website of the observatory and can be seen here On the right graphic, one can see the result of one night of observations. Four out of the five stars exhibits strong emission H-alpha line from the stellar disk with fine core absorption due to the star itself. Asymetry is probably due to radial velocity variablity (doppler effect) in the disk itself. HD168797 seems to have no emission, but we will need to plot a gaussian profil to check if the profile is purely photospheric.

HD179405 - 5 min exposure

HD179405 - addition of 10x 5min : 55 min exposure The H-alpha line emission is visible

Above, a raw image is shown. From raw image to calibrated spectrum profile, multiple steps of data reduction has to happened. They are all done with "amateur" freeware. Iris, by Christian, for pre-processing and Visual Spec by the author for calibration and spectral correction. Iris Website Visual Spec Website

When sky is not clear...

See the image below from Eric Frappa, a friend, and enjoy his website for more atmospheric outstanding images here

We had 4 nights over 7, which is not that bad. During some of them, we assisted to thunderstorm. When it reach the summit, it is no time to go out - electrostatic field is dangerous and thunder can fall anywhere on the summit, specially on the TV 103 meters antenna. But when thunderstorm is far enought but still close to enjoy the thunder lights, then it is a marvelous spectacle, and safe...

Eric Frappa Copyright

More images from Christian here - with Canon 5D - like this one below

Nikon D70 - 800 ASA - 30 Sec

During the day...

The Pic du Midi Observatory is very famous for its solar world-class observations. So, why not try to get some views of our closest star? The materiel is a Personal Solar Telescope from Coronado, (H-alpha filter) with Solar Max for better contrast and the camera is just a standard Sony camorder, coupled with a 40mm eyepiece - All is on a GP-DX mount with Skysensor control.

Observation session, with Christian and Eric around, on the Telescope of 1 meter terrace. Acquisition is made with a PC connected to the camcorder, so focus is easier. A dark curtain is also helpful to look at the screen... Acquisition is made of around 600 images run. Images are then extracted one by one and stacked to enhance the constrat and reduce the noise. Protuberences can be seen as well as white active areas. All is determined by the magnetic field activity. Sun is supposed to be in quiet period (cycle is every 11 years) - but still some activity can be seen. It has to be noted that for better signal, the camescope has been turned into "nightshot" mode For some technical details on PST images, see my PST webpage

Conviviality...

It is now about 16 years that I come to this place, about one or twice a year. So, you finally have good friends there. Astronomy is not only a personal experience, it is also about teamwork and conviviality when all are waiting for the sky to be clear. With our friends from the Paris Observatory, we enjoyed a "french pancake" party, at 2800m, at about 12 degres, on the summit of the pyreneans ! Thanks to François Colas, the Astronomer and Cooking Chief - Solar observers from the coronograph dome were invited too.

Other day, other practices: the standard lunch at the cafeteria with the technicians of the observatory or a special diner with our collegues

But when the night is approaching, it is time to prepare, to take flat field and prepare our personal instrument as well.

Time for deep sky imaging...

I used my Nikon D70 in two different configuration. One with a zoom set at 70mm, f/3.5 - and one with a Perl Halley 70/400mm small refractor all in parallel to my refractor for guiding. All at 1000 ISO I'm using the skysensor control set-up for the equatorial mount, but the weight is too big so I needed to manually guided the exposure by keeping a guide star in a reticuled eyepiece manually. It requires some patience, and good clothes to stay outside with no move.  One nitght was at 4.7°C with some wind and that was tougth. Hopefully, you take period of rest and you can admire the milky way - with no moon - so bright that you can see your shadow and from time to time quite very bright shooting stars.

Milky way, with the 70mm f/4.5 - 27min Region above Sagittarius with, from top to bottom: - M16 nebula - M17 "omega nebula" - Open Clusters M25 (left) & M23 (Right) - M20 "Trifide Nebula" - M22 cluster - M8 "Lagoon nebula"

Galaxie seen disk side with dust NGC891 Refractor 70/400mm 18 min exposure

"Pipe Nebula" - in 42 Ophucius region 70mm - 30 min exposure In the middle, the small "snake" dark nebula is visible, with M7 open cluster as well in the bottom left

"Dumbell" Planetary nebula - rest of a star explosion Hydrogene in Red - Oxygen and NH2 in green 400mm - 30 min exposure

M16 "Eagle Nebula" with open cluster NGC6605 400mm - 24 min exposure

"North America" nebula - In cygnus area 400mm - 18 min exposure

"Trifide Nebula" - M20 with M21 open clsuter 400mm - 15 min exposure

Double cluster of Perseus - HX perseus 400mm - 12 min exposure

But the best images are those from Christian, with Canon 350D modified to have more red color, with superbs lens. You can not miss his images on his website http://astrosurf.com/buil and more specially M8 Lagoon - M16 - Rho Oph region and Gamma Cygnii area

With a very good camera, a Canon5D I then used a Canon5D - with the same 70/400 refractor and a 135mm f/2.0 - Canon equipment is the one from Christian. All exposures with the 400mm are manually guided. Specially the 55 minute exposure (11 shots of 5 min each) was a "great" moment.

M17 - Omega nebula Canon 5D - 11 shots of 5 minutes - 55 minutes total exposure

"Veil Nebula" - NGC6992 Canon 5D with 400mm 6 shots of 5 min each Total exposure 30 minutes

Rho Ophiucus Region 135mm f/2 Canon 6 min exposure

Rho Ophiucus region Large view - 135mm f/2 First attempt of processing 6 shots of 1 min each Canon 5D

Night is over...

Light from the day shows up at 5:00pm. Time to finish up, takes the last picture or darks, admires Venus rising in the morning lights above Toulouse, and finally go to bed !

And get ready for the next sunset and night !