A sensitive all-sky camera for multipurpose
recording of the nightly sky down to 10th
magnitude
A. J. Castro-Tirado1, S. Vitek1 , P. Kubánek2 M. Jelı́nek1 , J. M. Trigo
Rodrı́guez3, A. de Ugarte Postigo1 , and T. J. Mateo Sanguino4
1
2
3
4
Instituto de Astrofı́sica de Andalucı́a (IAA-CSIC), P.O. Box 03004, E-18080
Granada, Spain
Ústav AV ČR, Ondřejov, Czech Republic
Institut Ciencies de l’Espai (ICE-CSIC), Campus UAB, Facultat de Ciencies,
Torre C-5, 08193 Bellaterra (Barcelona), Spain
Universidad de Huelva, Escuela Politécnica de la Rábida (DIESIA ), 21819 Palos
de la Frontera, Huelva, Spain
Summary. We present a novel design of an all-sky 4096 × 4096 pixels camera
devoted to continuous observations of the sky. A prototype camera is running at
the BOOTES-1 astronomical station in Huelva (Spain) since December 2002 and a
second one is working at the BOOTES-2 station in Málaga (Spain) since July 2004.
Scientific applications are the search for simultaneous optical emission associated to
gamma-ray bursts, study of meteor showers, and determination of possible areas for
meteorite recovery from the reconstruction of fireball trajectories. This last application requires that at least two such devices for simultaneously recording the sky
at distance of the order of ∼ 100 km. 15 GRB error boxes (13 for long/soft events
and 2 for short/hard GRBs) have been imaged simultaneously to the gamma-ray
emission, but no optical emission has been detected. Bright fireballs have been also
recorded, allowing the determination of trajectories, as in the case of the fireball of
30 July 2005. This device is a very promising instrument for continuous recording
of the night sky with moderate angular resolution and limiting magnitude (up to R
∼ 10), with additional non-astronomical applications.
1 Introduction
Continuous record of the sky is most essential to detect all kind of transient
phenomena ranging from cosmic gamma-ray bursts optical counterparts in
distant galaxies to variable stars in our Galaxy and meteor/fireball events
entering the Earth atmosphere. Although sensitive, continuous record of the
visible sky has been normally attempted just for monitoring of weather conditions on a given location, like an astronomical observatory. In general, these
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A. J. Castro-Tirado et al.
Fig. 1. The all-sky camera at the BOOTES-2 station in EELM-CSIC (Algarrobo
Costa, Málaga). A dew remover strip is placed around the fisheye lens in order to
prevent humidity condensing on the lens.
devices usually do not go deeper than R ∼ 4-6 mag, and therefore they are
severe limited for scientific purposes. Here we show a novel design of a large
format all-sky camera that we have developed in the context of the BOOTES
Project [1] under the auspices of INTA and that can be used for detecting
star-like objects as faint as R ∼ 10, having a time resolution of 1 min. The
first prototype started operations on 1 Dec 2002 at the BOOTES-1 station in
Huelva.
2 Design and instrument performance
Hardware. The device we have developed is based on a large format
optical CCD detector, like the Kodak K16801E, having 4,096 × 4,096 pixels
and 9 µm/pix with high quantum efficiency in the 4.000-9.500 Å range. A
wide-field lens, like a 16mm f/2.8 fisheye lens, is adapted through a specially
designed interface in order to image the full sky on the detector mentioned
above. The system is enshrouded on a specific housing (Fig. 1) and a dew
remover is placed around the lens in order to avoid condensation when the
humidity is in the range 90-100 %.
Software. A specific software has been also developed, in order to take
images during the whole night, and transfer them to a dedicated unit. The
CCD is controlled by tcshell script. Night sky frames expositions starts every
A sensitive all-sky camera reaching 10th magnitude
3
Fig. 2. A typical all-sky image (30 s exposure time) taken on a dark, cloudless
night at the BOOTES-1 station in INTA-CEDEA (El Arenosillo, Huelva). Limiting
magnitude is 10 towards the zenith and 8 close to the horizon. For clarity, blowups
at the position of the Pleiades open cluster and the Andromeda galaxy are shown.
full UT minute. The operations to be performed are based on the output from
the rts2-state program, which is part of the RTS2 package [2].
Data archiving. Acquired images (see Fig. 2) are saved on hard-disk
(HD) in FITS format. As the data gathered amounts up to 20 GB/night, it
is not possible to maintain the data on HD for a long time. Therefore, images
are stored on HD for 14 days only. A script, which is run from cron daemon,
ensures that images are deleted after that time. About 2% of the images are
removed on a daily basis, unless some astronomical event of interest would
have occurred. An archive is beeing kept to images taken every full hour are
being recorded on the All-Sky Permanent Archive (ASPA), which contains
data since December 2002. For a fast preview of the acquired images, we have
developed http access to the Archive. All images are converted onto JPEG
format (i.e. the size is reduced to 640x480 pixels) and stored in a long duration
archive.
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A. J. Castro-Tirado et al.
3 Applications
Application is multifold, ranging from GRB research to meteor and fireball
studies. The two all-sky cameras at the BOOTES-1 and -2 stations, have imaged 15 GRB error boxes (13 for long/soft events and 2 for short/hard GRBs)
simultaneously to the gamma-ray emission, but no optical emission has been
detected. In spite of this prompt optical emission reaching V = 9–10 mag
in several cases in the past (GRB 990123, GRB 060117, GRB 061007), our
all-sky cameras did not detect such a prompt optical emission in all the observations recorded so far, which points out that events like the ones mentioned
above do not occur so often [3].
Our all-sky CCD cameras can help to determine the magnitude of superbolides and study them even if the devices are located far away. An example is
the 30 June 2005 fireball recorded during double-station monitoring between
the two BOOTES stations spaced ∼ 240 km. Other examples of superbolides
recorded at large distances by our prototype were the 27 January 2003 and
the 30 July 2005 bolides [4,5]. These detections show the extraordinary capacity of this system to record distant ”meteorite-dropping” events that can
be tracked for estimating recovery areas. We hope the development of new
stations in the rest of Spain (in the context of the Spanish Patrol Meteor
Network [6]) will allow us the recovery of meteorites in the next future.
Additional applications are the surveillance of the sky on a given location,
in order to register commercial airplanes or artificial satellites. The monitoring
of the night cloud cover will also be of interest to astronomical observatories,
meteorological centres, etc.
Finally, we expect in the near future to make accessible the All-Sky Permanent Archive to other researchers, in order to facilitate the scientific exploitation of the data that we are continuosly gathering every night.
References
1. A. J. Castro-Tirado, J. Soldán, M. Bernas, P. Páta, T. Rezek et al: Astronomy
and Astrophysics Suppl. Ser., 138, 583 (1999).
2. P. Kubánek et al: RTS2: a powerful robotic observatory manager. In: Advanced
software and control for Astronomy, ed by H. Lewis and A. Bridger (SPIE–The
Intern´l Society for Optical Engineering, New York 2006), vol. 6274 (2006).
3. A. J. Castro-Tirado et al., in preparation (2007).
4. J. M. Trigo-Rodrı́guez, A. J. Castro-Tirado, J. Llorca, A. de Ugarte Postigo,
T. J. Mateo Sanguino, F. Gálvez: A superbolide recorded by the Spanish Fireball Network. In: WGN, Journal of the International Meteor Organization, vol
31(2), pp 49-52.
5. J. M. Trigo-Rodrı́guez, A. J. Castro-Tirado, M. Jelı́nek, S. Vitek, J. Llorca, J.
Fabregat: Two Likely Meteorite-dropping Bolides Recorded by a New High-Res
All-Sky CCD Camera. In: 37th Annual Lunar and Planetary Science Conference, pp 1559.
6. J. M. Trigo-Rodrı́guez et al: These Proceedings (2007).