Hindawi Publishing Corporation
Advances in Astronomy
Volume 2010, Article ID 869810, 7 pages
doi:10.1155/2010/869810
Research Article
T35: A Small Automatic Telescope for
Long-Term Observing Campaigns
Susana Martı́n-Ruiz,1 Francisco J. Aceituno,1 Miguel Abril,1 Luis P. Costillo,1
Antonio Garcı́a,1 José Luis de la Rosa,1 Isabel Bustamante,1, 2 Juan Gutierrez-Soto,1
Héctor Magán,1, 3 José Luis Ramos,1 and Marcos Ubierna1, 4
1 Instituto
de Astrofı́sica de Andalucı́a (CSIC), Camino Bajo de Huétor, 50. 18008 Granada, Spain
de las Ciencias, Avda de la Ciencia s/n, 18006 Granada, Spain
3 Centro Astronómico Hispano Alemán, C/ Jesús Durbán Remón 2-2, 04004 Almerı́a, Spain
4 SENER Ingenierı́a y Sistemas S.A., Avda. Zugazarte, 56. Las Arenas, 48930 Bizkaia, Spain
2 Parque
Correspondence should be addressed to Susana Martı́n-Ruiz, susana@iaa.es
Received 30 June 2009; Accepted 29 December 2009
Academic Editor: Lorraine Hanlon
Copyright © 2010 Susana Martı́n-Ruiz et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
′′
The T35 is a small telescope (14 ) equipped with a large format CCD camera installed in the Sierra Nevada Observatory (SNO)
in Southern Spain. This telescope will be a useful tool for the detecting and the studying of pulsating stars, particularly, in
open clusters. In this paper, we describe the automation process of the T35 and also show some images taken with the new
instrumentation.
1. Introduction
At the beginning, the main motivation for carrying out the
T35 project was the search for and the study of pulsational
behaviour of variable stars in open clusters. The role of open
clusters, as stellar associations with a common origin, is
fundamental in Asteroseismology. The physical properties
shared by the members of a cluster—distance, reddening,
age, and metallicity—provide us with very stringent
constraints on the models, complementing the information
obtained from the oscillation frequencies of the pulsating
stars. Exhaustive studies on the incidence of variability and
its behaviour, especially on pulsators located in the lower
part of the Instability Strip (γ Doradus, δ Scuti, or solar-type
variables), helps us to know better about some of the
fundamental parameters (Teff, log g, chemical composition
and rotational velocity) of these stars.
A previous systematic survey in search of γ Doradus
variability in different open clusters with different metallicities and ages was performed between the years 1995
and 2000 [1–3]. More than 340 nights of observation
at Sierra Nevada Observatory (SNO) (Granada, Spain),
using photoelectric photometry in the Strömgren-Crawford
system, were used to carry out this study. Nine γ Doradus
were found amongst the 41 variable stars detected in a sample
of 175 members distributed among the 10 open clusters
applying two methods based on different statistical tests to
classify our light curves. The main outcomes were that the
probability of finding γ Doradus stars increases if the sample
is restricted to AF-type stars (effective temperature between
6900 and 7200 K), luminosity class IV-V (stars in the main
sequence), and solar-type metallicity (Z = 0.02) and also
that this probability was not bounded to the age of the cluster
but to its metallicity, contradicting the theories published
by other authors. Although our results were very fruitful
due to the high precision of our uvbyβ measurements, that
is, less than two thousands of magnitude, the number of
member stars and clusters studied in the sample was small
with the addition of entailing an enormous observational
effort. Therefore, we needed a telescope of only modest
aperture (30–40 cm) to reach the desired S/N in a reasonable
time.
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Figure 2: The telescope and CCD Camera.
Figure 1: Dome of the T35 telescope.
With this telescope it is possible to perform long-term
observations of variable stars. Continuous observations in
time as well as long-time baseline campaigns are essential
to the study of variable stars, including binary systems and
pulsating stars. It is very difficult to allocate long duration
observing sessions on large telescopes.
The process of automation of the T35 has involved
efforts in hardware, software, and mechanics. A general block
diagram of the final system is shown in Figure 3, which is
described in detail in the next sections.
2. T35 Setup
The T35 telescope (Figure 1) is located at the Loma de Dı́lar
(2896 m altitude), near the central building of Sierra Nevada
Observatory (Granada, Spain). Before this 14′′ telescope
was installed, the dome housed a different instrument, and
therefore, first we had to restore and adapt the structure to
our new instrumentation.
The 14′′ Schmidt-Cassegrain telescope (35.56 cm) is a
Celestron CGE-1400. The telescope is equipped with an
SBIG STL-11000 CCD Camera with a KAI-11000M CCD
detector (4008 × 2762 pixels × 9 µm). Figure 2 shows both
instruments. The field of view is 31.70 × 21.14 arcmin with
a scale of 0.2475 arcsec per pixel. The camera has an internal
self-guiding camera Texas Instruments TC-237H (657 × 495
pixels × 7.4 µm) and an internal filter wheel with standard
UBVRI Johnson—Cousins filters.
Since the beginning, the aim of our project was to
install a telescope in order to perform long-term photometric
observing campaigns. Owing to the fact that the OSN
is a high mountain observatory where adverse weather
conditions happen frequently, the T35 telescope had to work
in remote mode with the greatest grade of autonomy. To date
we are working to get this objective and hope to robotize the
system in the near future.
Regardless of whether the mode of operation, fundamental requirements of pointing and tracking as well as a
minimum precision in the photometric measurements are
necessary. Table 1 shows these basic parameters necessary
for our objectives and those ones achieved in our telescope.
Table 1: Values of pointing, tracking and photometric accuracy
necessary for our scientific objectives and those achieved in the T35
telescope.
Pointing
Tracking
Photometric
accuracy
Scientific objectives
Better than 5′ of arc
0′′ of arc in several
min
1-2 thousandth of
mag
Achieved values
10′ of arc
1.′′ 3 of arc in 2 minutes
5-6 thousandth of mag
The photometric accuracy, the 5-6 thousands of magnitudes
have been obtained observing a variable star during a
nonphotometric night, taking the frames with binning 3 × 3,
and using faint comparison stars. Best outcomes, less than
2 mmag, can be achieved if the atmospheric conditions as
well as the observing parameters (integration time, binning,
etc.) are optimum. Respect to the tracking accuracy, it can
be improved using the internal self-guiding camera but
the small size of chip does not often allow us to find
a bright star in the camera field of view. In order to
solve this problem, an external autoguiding system is being
implemented. To obtain a higher value of pointing accuracy
is more complicated. The typical pointing values have been
obtained using around 30 stars located in different positions
in the sky. The telescope pointed out 10′ of arc in 23% of
the cases. To accurately point to objects, first we preformed
the alignment procedure described in the telescope manual
using two known stars. Although the telescope was aligned
properly, a pointing model was created to improve even more
the pointing precision. This model has been made using the
application TPoint which works quite well with the telescope
control programe TheSky Astronomy Software. Although the
observed target falls inside the field of view of the camera, its
position can be corrected by the user at the beginning of the
observation.
The T35 telescope has been supported with funding
from the Marie Curie Reintegration Grant “Detection and
Survey of pulsating Star in Open Clusters: a step forwards in
Asteroseismology” (MERG-CT-2004-513610) funded from
the European Commission’s Sixth Framework and from
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the Spanish project “Participación española en la misión
espacial CoRoT” (ESP2004-03855-C03-01).
10 bit
Encoder
3. Control System
As mentioned above, the objective of this project was to
automate and control remotely the movement of telescope
and dome. The dome control system, in particular, is
required to implement the following functions:
(2) ability to move to an absolute position, from 0 to 359
degrees,
Telescope
control
system
(TCS)
RS-232
(3) ability to move to a relative position (± xxx degrees),
(5) management of a zero cross-reference position for
loss of steps error detection,
(6) ability to modify remotely the constants of operation
(park position, inertia constant, zero-cross position,
etc.),
(7) measurements of consumption, and ability to detect
a malfunction of the system through measurement of
anomalous values.
As can be seen in Figure 3, both telescope and dome
can be controlled locally from a notebook or a conventional
PC installed inside the dome (Telescope Control System,
hereafter TCS). However, the control of the system in usual
operation is performed from one of the user computers in
the main building of the observatory.
Regarding hardware elements, in this application both
commercial (zero cross-sensor, encoder, and dome motor)
and in-house developments (consumption measurement
card, dome controller) have been used.
With respect to software, at least two programs were
needed for this application, one to run on the Dome Controller (DC) and another on the TCS or user computer. Apart
from these, an engineering program was also developed for
technical purposes.
The main mechanical works were related to the design
and fabrication of adaptors for the integration of the different
elements in the dome, in order to assure a proper reading
of the encoder and the zero cross-sensor minimizing loss of
steps.
In the next sections, the main tasks, elements, and programs developed for this application are discussed in more
detail.
3.1. Hardware. The user interface and main control of both
telescope and dome are provided by TCS, which is connected
to the Internet in order to allow the system to be controlled
remotely. In practice, the system is controlled from the main
user computer on the T90 console. The TCS is connected via
RS-232C to the telescope and the DC.
The DC, developed specifically for this application, is
based on a PIC18F458 microcontroller, in which we had
experience from previous projects as regards programming
Zero
cross
sensor
RS-232
(1) continuous reading and updating of Azimuth (Az),
(4) ability to move to a prefixed park position,
Dome motor
Dome
controller
(DC)
Consumption
measurement card
Telescope
celestron
CGE-1400
Internet
User
computer
in T90
console
Figure 3: General block diagram of the system.
and developing [4]. There exist several commercial modules
for control of small and medium-sized domes. However, the
solution chosen was based on a modular system designed
in the Instituto de Astrofı́sica de Andalucı́a and used in
previous projects. This solution presents several advantages
over a commercial system. An in-house design is well
known and documented, and therefore, it is easier to
maintain. It allows for an exact adaption to particular
requirements at a low price. The heart of the system, the
microcontroller PIC18F458, can be easily programmed in
high-level languages using different tools supplied by the
manufacturer or third party providers. Finally, the design’s
modularity made it compatible and interchangeable with
other modules used in our institution. These factors can
make this DC attractive for other telescopes, provided that
their requirements are similar to those of our system. In fact,
the advantages associated to this in-house developed system
(modularity, ease of programming, and price) can result in
interest for other institutions, not only to develop their own
dome controller, but also other systems whose requirements
are affordable by the PIC18F458 microcontroller.
As can be seen in Figures 3, 4 and 5, the DC reads
the dome position from an absolute Gray encoder with a
resolution of 10 bits (Hohner, model CS10-81310311-1024).
A zero cross sensor allows for loss of steps error detection.
The system also employs a consumption reading card, used
to detect and prevent breakdowns due to ice on the dome or
malfunction of the motor.
In addition to the reading of the encoder and the zero
cross-sensor, the DC performs actions on the dome motor.
The DC uses a driver card for adaption of the control signals
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Dome controller (DC)
220 V AC
Power
supply
220 V AC
Power
supply
10 bits
absolute
gray
encoder
PIC18F458
CPU card
(E-C17)
Drivers’ and
optocouplers’
board
(E-C40)
Analog
input
board
(E-C44)
TCS
RS-232
AZ+/AZ− keys
(manual
control)
Dome
motor
Consumption
reading card
(E-C45)
Zero
cross
sensor
Figure 4: Connections among the different elements used in the dome control.
CPU board +
drivers & analog
inputs boards
(below)
10 bit absolute
encoder
Dome controller
(DC)
Power supply
Cable to the
zero crosssensor
Manual
movement
controls
Transformer
Figure 5: Photograph showing part of the system hardware. Red
text show elements developed and described in this work.
Figure 6: Interior of the Dome Controller (DC), showing its different boards and elements.
to the levels needed for acting on the dome motor. In order
to facilitate the use of the previous operating hardware, the
DC acts in parallel with buttons AZ+ and AZ−, which allow
for manual movement of the dome. Consequently, there is
no need for flipping between a manual and an automatic
mode of operation. Figures 3 to 6 show a general block
diagram of the system and some pictures of its hardware
implementation.
written in C, using a PICC compiler integrated in the
MPLAB environment. The program handles the acquisition
of data from the absolute encoder, zero cross-sensor, and
consumption reading card. In response to the read values,
it calculates the dome target position and generates the
necessary signals for the control of the motor. DC and
TCS are connected through an RS-232 link, using control
commands and data packets in accordance with a protocol defined by the authors and described in the next
section.
The ASCOM Platform includes an application called
ASCOM Dome Control Panel, which is a simple dome
control “middleware”. It provides a uniform and consistent
interface, regardless of the actual hardware and connections
used. In our application, it was necessary to develop a driver
that translates the ASCOM Dome interface to our software
RS-232 commands (see Section 3.2.2 below).
3.2. Software. The Control Software of this automatic telescope is based on the ASCOM (Astronomy Common Object
Model) standards. The telescope, the CCD camera, and the
filter wheel are ASCOM compliant, so the manufacturers
provide the corresponding ASCOM driver interfaces.
Regarding the DC, a program for the 18F458 microcontroller has been developed. The source code has been
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Figure 7: Graphic user interface of the engineering program developed for technical purposes.
Although dome control is usually performed through
the ASCOM Dome interface, an additional engineering
program has been developed in LabVIEW (see Figure 7).
This program will not be running during the usual operation
of the system. It only needs to be executed eventually when a
closer monitoring of the control and data packets is desired.
This result is useful when trying to fix a breakdown, checking
the correct operation, or implementing new features in the
system. As can be seen, the graphic interface displays all the
information about the dome status and allows for sending
all the control commands. In the upper right corner it
displays the present position of the dome, which is updated
continuously with the values read from the encoder. In
addition to the different buttons that perform the various
commands, there is a command line available where a
user can write directly the command in the format shown
in Table 2. In order to detect interrupts and failures in
the communication, all the traffic in the RS-232 link is
monitored in the upper right line. Error conditions and zero
crosses are also displayed using a pair of LEDs and a text
window, where the type of error is displayed.
3.2.1. Communication Protocol. Communication between
TCS and DC is bidirectional, messages structured according
to the following format:
<STX><command><arguments><CR><LF><ETX>
where <STX>, <CR>, <LF> and <ETX> are the next ASCII
control characters:
<STX>: Start of transmission (hexadecimal: 02h)
<ETX>: End of Transmission (03h)
<LF>: Line Feed (0Ah)
<CR>: Carriage Return (0Dh)
In order to make visualization of messages easier,
both commands and arguments are written in ASCII.
<command> has a fixed length of 4 bytes, while <argument>
is variable, depending on the command. Table 2 lists all the
messages used in the communication, showing the fields
<command><argument> but not the control characters. As
can be seen, in many of these, <argument> consists of the
present or target azimuth, which appear in the table as
xxx.
3.2.2. ASCOM Dome Driver. ASCOM is a platform that
utilizes a standard interface between astronomic devices and
their control software. Any device supplied with an ASCOM
driver can be controlled by any ASCOM compliant software.
In our application, every element supplied with the telescope
(CCD, filter wheel, and the telescope itself) included an
ASCOM driver. Thus, the main effort in development had
to be focused on the dome controller. From the software
development point of view, the main task consisted of
programming a dynamic link library (DLL) for Windows.
Any language suitable for developing Windows objects
(COM) can be used. In this application we used C++, in a
Microsoft Visual C++ 6.0 compiler.
As we have seen before, communication between the
TCS and DC is achieved through a serial link based in the
RS-232 standard. Thus, it was also necessary to integrate a
serial communication library in the project. We chose for this
purpose a freeware code Serial Communication for WIN32,
nonevent driven version [5] performing the modifications
needed to meet our requirements and to follow our serial
message format.
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Advances in Astronomy
Table 2: Description of messages used in the communication
between TCS and DC.
Message
AZABxxx
AZR+xxx
AZR−xxx
PARK
STOP
¿AZ?
¿ST?
¿EE?
¿CO?
AOFF
A AZ
A CO
A ZE
CPARxxx
CZERxxx
CZEMxxx
CINExxx
FIN!xxx
¡ZE!xxx
¡AZ!xxx
¡ST!
¡EE!
¡CO!
PAR!xxx
ZER!xxx
ZERM!xxx
INE!xxx
ERR!
Messages from TCS to DC
Meaning
Absolute movement to azimuth xxx
Relative movement (+xxx or −xxx degrees)
Movement to the PARK position
Stops dome movement if it is in motion
Requires present azimuth, status, EEPROM content,
motor consumption.
Auto messages disabled
Auto azimuth, auto consumption, auto zero cross
messages enabled.
TCS sends new values for park position, zero cross
position, zero margin constant, inertia constant.
Figure 8: IC 434 and M42 images obtained by using the T35
telescope.
Messages from DC to TCS
Last command executed, dome stopped at azimuth
xxx.
Zero cross detected at azimuth xxx
Present azimuth, status, EEPROM contents,
consumption. These messages are sent in response to
¿AZ? ¿ST? ¿EE? ¿CO? or as automatic information, if
the corresponding option is enabled.
Confirmation of new values for park position, zero
position, zero margin or inertia constant, sent by
TCS through commands CPARxxx, CZERxxx,
CZEMxxx and CINExxx.
Error message. The type of error is codified in the
<argument> field.
Once developed this ASCOM driver, the dome could
be controlled through any ASCOM compliant software, like
MaxIm DL, TheSky Astronomy Software, or ACP Observatory
Control. ASCOM platform also provides a small software
packet for dome control, called ASCOM DOME Control
Panel, which is the one we used in our application.
4. First Results
After installing the new instrument, some spectacular images
of some objects in the sky were taken. Figures 8 and
9 show images of the IC434 bright red emission nebula
around the Horsehead and of the M42 Great Nebula of
Orion. The first one is a BVR median combination of
20 × 60 seconds of exposures and the second image is
a combination of 5 × 60 seconds of exposures through
BVI filters. Other images can be seen in the web site
http://www.osn.iaa.es/T35/galeria img.html.
Figure 9: IC 434 and M42 images obtained by using the T35
telescope.
Recently, we have carried out several photometric
observing campaigns. The IC4756 and NGC7243 open
clusters as well as two eclipsing binary systems, HIP7666
and V994Her, were observed during the summer and winter
of 2008. This data is being reduced and the results will be
published soon.
5. Conclusions
We have attained to install and automate a 14′′ telescope system in order to perform long-term photometric campaigns.
Although the telescope presented some problems of pointing
and tracking during the first observations, the behaviour of
the telescope and dome control was quite optimum. Both
parameters improved fairly when a telescope pointing model
was used. The new external autoguiding system will increase
the tracking precision considerably.
The control of the telescope system has been performed
through standard ASCOM commands. A simple system
based on microprocessor has been designed and implemented allowing the control of the nonstandard dome using
Advances in Astronomy
ASCOM compliant software. Therefore, due to its reliability,
this system is being adapted to the two other domes of the
SNO.
The control of both telescope and dome can be performed locally or remotely, with the latter being the usual
mode of operation. The possibility of controlling the system
from the facilities of Instituto de Astrofı́sica de Andalucı́a, in
the town of Granada, implies an important logistic advantage
and considerable time saving.
Acknowledgments
We would like to acknowledge the staff in SNO for his
technical, logistic, and human support. The first author
thanks Juan Gutiérrez-Soto for his help with the data
reductions and Victor Costa, Rafael Garrido, José Luis Ortiz,
and Lourdes Verdes- Montenegro for their useful support.
References
[1] S. Martı́n-Ruiz, “γ Doradus-type variability in Open Clusters,”
Ph.D. thesis, Granada University, 2000.
[2] S. Martı́n and E. Rodrı́guez, “Search for γ Doradus variable
stars in the Pleiades cluster,” Astronomy and Astrophysics, vol.
358, no. 1, pp. 287–298, 2000.
[3] S. Martı́n, “Survey in search of variable stars in open clusters,”
in Interplay of Priodic, Cyclic and Stochastic Variability in
Selected Areas of the H-R Diagram, C. Sterken, Ed., vol. 292 of
ASP Conference Series, pp. 58–64, 2003.
[4] L. P. Costillo, J. M. Ibáñez, B. Aparicio, and A. J. Garcı́a,
“SNOWS: Sierra Nevada observatory weather system,” in
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Proceedings of SPIE, Orlando, Fla, USA, May 2006.
[5] T. Schneider, 2001,http://www.tetraedre.com/advanced/serial
.php.
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