The Role of Small Telescopes in Modern Astronomy

October 14-October 15, 1996

Poster Abstracts

Observations of T Tauri Stars and Supernovae with the 0.6 m Telescope at Van Vleck Observatory

William Herbst, Katherine Rhode, Aaron Steinhauer and Adam Heinlein
Astronomy Dept., Wesleyan University

The 0.6 m telescope at Van Vleck Obs. on the campus of Wesleyan University has been used since 1991 to monitor portions of the Orion Nebula Cluster in the Cousins I band. About 600 stars are monitored each year. We also monitor bright supernovae. Undergraduate students do most of the observing, data reduction and analysis. Here we highlight the discovery of additional rotation periods and an updated version of the bimodal period distribution based on five years of monitoring the ONC. We have also detected some stars which show rapid declines in brightness similar to what is expected for an eclipsing binary. No definite periods have yet been found, however. SN 1994ae was observed extensively at Wesleyan in BVRI. An image taken after the supernova faded has allowed us to carefully correct the photometry for contamination by the host galaxy. Light curves in all four colors are presented. Since this is a Type Ia supernova, the data will be useful in addressing issues such as the homogeneity of Type Ia light curves and the calibration of the Hubble constant.

Finding Variables with Small Telescopes

A. Henden (, R. Stone (
USRA/U.S. Naval Observatory, Flagstaff Station, P.O. Box 1149, Flagstaff AZ 86002 USA

While strictly outside of the aperture-size restrictions of this workshop, we present a variable star survey undertaken with the USNO 0.2m FASTT telescope as an example of one project that most small telescopes can perform.

The FASTT telescope is a completely automated transit instrument equipped with a 2048x2048 CCD and a 50arcmin field of view. Each pixel is 1.5arcsec in size; the telescope is defocussed so that the image FWHM is typically 3arcsec, thereby removing the undersampling and improving the astrometry and photometry. The FASTT and scanning techniques are discussed in detail in Stone et al. (1991, AJ, 111, 1721).

The original motivation for the 0.2m survey of 16 regions arranged along the celestial equator was to set up astrometric calibration regions for the SDSS survey discussed by Gunn and Knapp (1993 ASP Conf. Series 43, p267). Each region is approximately 3.2 x 7.5 degrees in size, for a total area of 24 square degrees per region or 384 square degrees for the survey. Each region was scanned in 50arcmin strips, with 202 seconds of integration per object within the strip. Strips were overlapped center-to-edge, and block adjustment reductions used to tie scans into a common reference system. Mean positions for the 679,866 stars included in the survey regions are known to better than 50mas; mean photometry for the non-variable objects is accurate to ±0.02 mag.

The methods used to compute the magnitudes needs further discussion. Namely, standards from Landolt and the Harvard E-fields were observed with the FASTT in order to set up a grid of secondary standards with accuracies of ±0.008 mag. These standards were observed each night and used in the usual reductions to compute magnitude zero-point and primary extinction values that, in turn, were used to reduce all aperture readings to a FASTT instrumental system, hereby designed by R8, which closely matches the SDSS r'-passband and is similar to the Cousin's R-passband. If (V - R) colors should become available, then the FASTT R8 magnitudes can be converted to true R magnitudes using the transformation given in Stone and Pier (1996, BAAS 27, 1389).

Except for obvious blends, the number of stars observed in each SDSS field are reasonably complete down to an apparent magnitude of R8~17. The four fields E, F, M, and N are exceptions. These fields are at low Galactic latitude and contain very high densities of stars. In order to reduce the processing, these fields are only complete to R8~14 mag; however, fainter stars were observed in subareas of these zones down to the limiting magnitude of the FASTT. These subareas comprise 17% of the total area observed in these zones.

Efforts were made to observe SDSS fields only on nights of good photometric quality, in that nights with high levels of extinction were eliminated. Many of the nights were photometric or mostly photometric during the observing time. The photometric nights were identified by comparing individual nights, where differences in magnitudes would be very small if both of the nights were photometric. Mean magnitudes and standard errors were then formed for all stars observed on photometric nights. In general, these means were computed from 5.5 to 8.6 measures obtained on different nights. The formal accuracy of these magnitudes is ±0.015 mag, and their rms-scatter is ±0.03 mag, except for the faintest stars where the scatter is ±0.12 mag.

Three criteria were used to identify variables: photometry, astrometry, and image profiles. If the rms-scatter was larger than 3 X the expected error in the magnitude, then the star was identified as a possible variable. This initial cut yielded 4000 potential variables. However, it was found that many of these stars were actually close pairs which appeared as single stars on nights of good seeing and blends on nights of poorer seeing, causing the observed magnitudes to falsely vary. Fortunately, there is good astrometry for all of the SDSS calibration stars, and these false variables can be often identified as those stars with large astrometric errors. Possible variables with 5-σ or greater X the expected errors in their positions were removed from sample as likely misidentifications. The astrometric error criteria reduced the number of potential variables to 2060. A final cut was made by removing those possible variables that had only one discrepant photometric measure, and for whom the ratio of FWHM in x and y for that measure was more than 2-σ from the mean for the star. This usually indicated that some instrumental problem occurred on that night, or that a blend occurred that did not strongly affect the image centroid. This criteria rejected an additional 223 candidates. We then used non-photometric nights and differential techniques to extend the amount of photometry for each variable, resulting in 8-10 total measures per variable in the survey.

A total of 1837 variable stars have been identified. Outside of fields E,F,M and N, where we do not do complete sampling, there are 55 previously known variables and 770 new variables in the remaining 12 fields. Of the known variables, we identify 35. Of the remaining 20, 15 are either too bright or too faint for detection, and 5 are missed for some other reason. This means that 96 percent of the detected variables in this survey are previously unknown. The variables constitute 0.3 percent on average of all the stars identified in this survey. If this ratio of new/old variables is held, and since our survey only covers 1percent of the sky and avoids most of the galactic plane, then such a telescope (or pair of telescopes) surveying the entire sky would detect many tens of thousands of new variables in our galaxy.

More information about the survey, or a list of variables within a particular category, can be obtained from the authors. While we intend to investigate small subsets of these variables, the majority are available to interested observers. Note that these stars are true variables, have accurate coordinates, an estimate of the variable type, light curve and period, and have excellent finding charts.

The Eight-Inch CCD Astrograph

Marvin E. Germain (
U.S.Naval Observatory

The USNO Eight-Inch CCD Astrograph is a robotic, refracting telescope currently under development for the purpose of conducting an all-sky, astrometric survey to 16th magnitude with an anticipated mean error of 30 mas. While initially intended for photographic astrometry, the tail piece has been fitted with a 1K by 1.5K CCD camera for test purposes. This will soon be replaced by a 4K by 4K camera, allowing imaging of one square degree. The pixels are 9 microns square, resulting in three pixels across an image when the seeing is one arcsecond. A 4.5- magnitude diffraction grating has been installed at the entrance pupil, giving the system a dynamic range of about 10.0 magnitudes. This telescope features a fully-automated mount. The dome, an X-Y slide, and the focus are also set automatically. The X-Y slide, which is attached to a separate guide scope, allows guiding on stars at any position in the field. Guiding is done with an SBIG ST-4 autoguider. The system is controlled from a PC via an embedded single-board computer. It has an advanced, red- corrected lens developed in the University of Arizona Optical Sciences Department achieving nearly diffraction-limited imaging over a nine-degree flat field.

Eclipsing Binary Research and Education at Baker Observatory

George W. Wolf
SW Missouri State University

I. The Facility - Baker Observatory

At SW Missouri State University the Department of Physics and Astronomy operates the Baker Observatory, which is located 25 miles northeast of Springfield, Missouri at a dark site. The land for the Observatory and funding to get it started were donated in 1977 by William and Retha Stone Baker. The 40-acre site is located in an agricultural area and is well protected from population encroachment and the concurrent light-pollution. A single story, three room building constructed of reinforced concrete holds two Ash domes to protect the two permanently mounted telescopes. A concrete observing pad south of the building with piers for 12 portable 8-inch telescopes is used by evening astronomy labs. Several years ago the Bakers helped with the purchase of a small farm adjoining the observatory; its farmhouse is now used as sleeping quarters for the student and faculty observers.

II. The Small Telescopes and Instrumentation

The main research telescope, mounted in a 4.3 meter diameter Ash dome, is the refurbished 0.4-m Cassegrain reflecting telescope formerly known as the #2 16-inch at Cerro Tololo, now on long-term loan to SMSU. The mirrors have been re-coated, the entire electrical system has been re-wired, and the tube and mount repainted. The f/18.75 optical system was designed for the purpose of photometry, and is still in excellent condition. An electric motor is used to move the secondary mirror for focussing purposes. The equatorial mount consists of a torque tube polar axle with an offset declination counterweight arm, and provides excellent mechanical stability.

From 1990 to 1992 an NSF equipment grant (AST-9001360) was used to upgrade the drive system of the telescope and to add a CCD guider for long exposures. Positioning and guidance of the telescope have been modernized by installation of a computer-controlled closed-loop system utilizing stepping motors and optical angle encoders for both axes of the telescope. Micro-stepping motors (from Parker-Compumotor, Inc.) are being used to allow fast and slow positioning, as well as open-loop tracking.

The main CCD camera system was purchased in June 1989, and consists of a Photometrics Ltd. PM512, grade A CCD, liquid nitrogen cooled camera head, a 4 Mbyte image buffer and video monitor system, and associated camera electronics. The 512 x 512 pixel, metachrome-coated CCD has a resolution of 0.54 arc seconds per pixel and a field size of 4.6 arc minutes on the 0.4-m telescope. It has a deep full-well (250,000 electrons) and a read noise of less than eight electrons. A twelve-hole, rotating filter wheel is positioned by a computer command to a small stepping motor and contains CCD optimized UBVRI and uvby,H-beta filters.

A second research telescope, mounted in its own 3.1 meter Ash dome, is a 0.36 meter Celestron Schmidt-Cassegrain with a retrofit Byers drive. During the past year a Photometrics Star I thermoelectrically-cooled CCD system with a Thomson scientific-grade, metachrome-coated, 384x576 pixel CCD and fully configured computer has been mated with an eye-piece box and automated UBVRI filter wheel to provide a second complete CCD photometry system on this telescope. The f/11 optics are much faster than those of the 0.4 meter and permits the imaging of 10 arcminute wide fields with a small penalty in light gathering power and stability.

III. The Research

Among the known, longer-period, double-lined spectroscopic binaries there may be many, as yet undiscovered, eclipsing systems. The discovery of eclipses and the subsequent analysis of the observed light curves in such systems would add significantly to our knowledge of stellar masses. Also, among the longer-period, double-lined spectroscopic systems already known to be eclipsing are many that have no modern light curves. For the past three years at the Baker Observatory we have been conducting a survey (1) to search for eclipses in spectroscopic systems that appear promising for one reason or another and (2) to obtain modern light curves for neglected longer-period eclipsing systems with double-line spectroscopic solutions.

We have thus far observed with the Photometrics CCD system on the 0.4 meter telescope 49 double-line spectroscopic systems, ten of which are known to have eclipses. Most of the light curves have been obtained in the B,V,R and I filter regions (or just the V,R, and I for some stars). As would be expected in such a survey, most of the systems without known eclipses have still not been found to eclipse, although some have shown variability. Since this survey is still in progress and most of the systems have only been observed at intermittent phases, no definite statements can yet be made for them. Two systems which may have been found to eclipse are HD 82780 and HD 208095.

IV. The Education

SMSU has been a member of the NASA-supported Missouri Space Grant Consortium for the past five years and receives funding for undergraduate and high school student internships for interns assisting in astronomical research. During the academic year we can generally have three of four undergraduate interns and during the summer we usually have three undergraduate and three high school interns. Since the NASA Space Grant Program emphasizes the need to involve women and minorities in the research, at least half of our interns during the past few years have been women. The NASA supported undergraduate interns, and high school interns during the summer, have been involved in all aspects of this research project. Each student has worked at the observatory obtaining data while using the CCD camera and telescope, has learned to use IRAF on the astronomy workstation at the university and has had the opportunity to reduce and analyze the data obtained. And finally, all interns have delivered talks on an aspect of their research participation at annual state-level Missouri Space Grant Consortium meetings and have written corresponding research papers, which were published in a bound volume and made available at those same state meetings.

V. Acknowledgements

This research is supported by NSF grant AST-9315061 and the interns by NASA grant NGT-40029.

Large-Scale Structure with a Small Telescope

Eric G. Hintz1,2 (, J. Ward Moody1 (, Michael D. Joner1 (, Michael Rice1 (, and Kenneth A. Nelson1 (
Department of Physics and Astronomy
Brigham Young University
263 FB
Provo, UT 84602

We have used the Burrell Schmidt Telescope, which is a 0.6/0.9-m telescope, to probe the large-scale structure of the Universe. We have examined rich Abell clusters of galaxies in an attempt to understand their formation and evolutionary histories. We found that luminosity functions of the six clusters we examined showed no significant differences. However, a new quantitative morphological system we have developed showed differences based on the Rood-Sastry type of the cluster. A cD cluster showed more extended objects, while a L cluster showed more compact objects. We believe these differences can be traced directly to the clusters environment and evolution. We are now extending this work to look at more clusters selected based on their Rood-Sastry type and another set selected based on the clusters position within a supercluster.

We have also used the Burrell Schmidt to examine the Boötes Void region in order to determine just how empty it is. We have examined over 100,000 objects in the direction of the Void, down to a magnitude limit of 22.0, and a completeness limit of 20th magnitude. Our data suggests the Boötes Void should be redefined to the southwest of its originally defined location. With this new center we find the Boötes Void to be a completely empty corridor stretching for 460 Mpc at a position of α = 14h15m and Δ = +42o.5, and having a range in redshifts from cz = 3,000km/sec to cz = 40,000km/sec.

We feel that small telescopes, such as the Burrell, can contribute greatly to studies of the large-scale structure of the Universe, and in some cases do things the larger telescopes just cannot do.

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1Bear Lake Observatory Post-Doctoral Fellow.
2Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatories, operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. Observations made with the Burrell Schmidt Telescope of the Warner and Swasey Observatory, Case Western Reserve University.

McDonald Observatory: Two Niches for Small Telescopes

Thomas G. Barnes III
McDonald Observatory, The University of Texas at Austin

This paper addresses the role of small telescopes at McDonald Observatory. Given availability of 9.2-m , 2.7-m and 2.1-m telescopes at McDonald, demand for our 91-cm and 76-cm telescopes had declined. In addition, the decision to devote our reduced resources to the larger telescopes affected the role of the smaller ones.

The implications seemed clear to us: only do science on the smaller telescopes which is not possible on the larger telescopes and minimize the demand for resources from the smaller telescopes.

The 91-cm telescope has accordingly been restricted to photoelectric photometry on programs which involve coordinated observing with other McDonald telescopes, simultaneous observing with satellites or other observatories, multiple-week observing runs and target of opportunity programs.

The 76-cm telescope has been dedicated to a prime focus CCD camera. This f/3 camera has a field of view 46.5 arcminutes square and an R limit (3 sigma) of 22 mag. With autoguiding from an auxiliary telescope and a servo-controlled focus, the telescope is ideal for wide field imaging, synoptic and survey programs, and solar system astrometry.