Automated Photoelectric Telescope Research Articles

Starspot photometry with robotic telescopes. $UBV(RI)_{\rm C}$ and by light curves of 47 active stars in 1996/97

We present continuous multicolor photometry for 47 stars from October 1996 through June 1997. Altogether, 7073 V (RI)c, UBV ,a ndby data points, each the average of three individual readings, were acquired with three automatic photoelectric telescopes (APTs) at Fairborn Observatory in southern Arizona. Most of our targets are chromospherically active single and binary stars of spectral type G to K but there are also four pre-main-sequence objects and three pulsating stars in our sample. The light variability is generally due to rotational modulation of an asymmetrically spotted stellar surface and therefore precise rotational periods and their seasonal variations are determined from Fourier analysis. We also report on photometric variations of CrB (A0V) with a period of 0.44534 days. All data are available in numerical form.

Techniques for Automated High‐Precision Photometry of Sun‐like Stars

ABSTRACTTennessee State University operates several Automatic Photoelectric Telescopes (APTs) located at Fairborn Observatory in the Patagonia Mountains of southern Arizona. The APTs are dedicated to photometric monitoring programs that would be difficult and expensive to accomplish without the advantages provided by automation. I describe the operation of two of the telescopes (0.75 and 0.80 m APTs) and the quality‐control techniques that result in their routine acquisition of single‐star differential photometry with a precision of 0.001 mag for single observations and 0.0001–0.0002 mag for seasonal means. I show that a primary obstacle to photometry at this level of precision is intrinsic variability in the comparison stars. Finally, I illustrate the capabilities of the APTs with sample results from a program to measure luminosity cycles in Sun‐like stars and a related effort to search for extrasolar planets around these stars.

Starspot photometry with robotic telescopes

We report on the progress of our ongoing photometric monitoring program of spotted late-type stars with automatic photoelectric telescopes (APTs) on Mt. Hopkins in Arizona and on Mt. Etna in Sicily. We present 9 250 differential UBV and/or observations for altogether 23 chromospherically active stars, singles and binaries, pre main sequence and post main sequence, taken between 1991 and 1996. The variability mechanism of our target stars is mostly rotational modulation by an asymmetrically spotted stellar surface. Therefore, precise rotational periods and their seasonal variations are determined using baselines between 3 years for HD 129333 to 34 years for V410 Tauri. We report the largest V light-curve amplitude of any spotted star observed to date: for V410 Tau in 1994–95. Long-term variations of the overall light levels of our target stars are sometimes of similar amplitude as the rotational modulation itself and are most likely caused by an analog of the solar 11-year spot cycle but mostly without a well-defined periodicity. For some of our target stars (HD 12545, HD 17433, EI Eri, V410 Tau, LQ Hya, and HD 106225) we estimate a probable cycle period. A complete light curve of the semi-regular S-type giant HR Pegasii is presented. All data are available via the WorldWideWeb.

WOLFGANG-AMADEUS: THE UNIVERSITY OF VIENNA TWIN AUTOMATIC PHOTOELECTRIC TELESCOPE

ABSTRACT We describe the University of Vienna twin automatic photoelectric telescope (APT) located at the new Fairborn Observatory at Washington Camp in southern Arizona. Not only are the telescopes fully automatic, also the observatory itself is automatic. A site-control computer monitors weather sensors and operates the roof while the telescope control computer operates the photometer and accepts input files from and provides nightly observations to the astronomer; no direct operating personnel is needed. Both telescopes have 0.75-m primary mirrors, a CCD finder camera, and an environmentally controlled single-channel photoelectric photometer with filter combinations optimized for use in the blue (Wolfgang) and in the red (Amadeus) wavelength for asteroseismology of non-radially pulsating variables, and for monitoring asymtotic-giant-branch stars. Some first results are presented.

Properties of Sun‐like Stars with Planets: 51 Pegasi, 47 Ursae Majoris, 70 Virginis, and HD 114762

Radial velocity variations have revealed planets orbiting 51 Peg, 47 UMa, and 70 Vir, and a low-mass companion orbiting HD 114762. We analyze parallel records of photometric measurements in Stromgren b and y and Johnson V, R, and I passbands and Ca II H and K fluxes in those stars. In the case of 51 Peg, the high precision of the differential photometric measurements made by the 0.75 m Automatic Photoelectric Telescope and the nonvariability of the star would allow the detection of a transit of a planet as small as Earth (corresponding to an amplitude of 0.0001 mag) if its orbit were nearly coplanar with our line of sight. No transits were observed. For 51 Peg and 70 Vir, the upper limit of nondetection of photometric variability at their companion's orbital periods is Δ(b + y)/2 < 0.0002 ± 0.0002 mag. For HD 114762, it is ΔV < 0.0007 ± 0.0004 mag. Such small amplitudes of photometric variability seem to eliminate periodic velocity variations expected from p-mode oscillations. All four stars are magnetically quiet; that is, they lack the typical Ca II and photometric variability due to rotation and activity cycles expected from surface magnetic activity in solar-type stars. Such quiescence produces an interesting observational bias that favors the detection of planets from low-amplitude radial velocity or photometric variations by minimizing the contribution from intrinsic stellar variability. We discuss the circumstances for which the probability of planet detections is improved by the reduced level of variability from surface magnetic activity in G and K stars. Stars with low variability in surface activity should be the best candidates for planet searches using radial velocity and photometric techniques. Searches for planets around younger, more active stars will be impeded by variations in velocity or brightness caused by time-varying surface features. The Ca II H and K fluxes indicate that all four stars are older than 5 Gyr. Ages were estimated from the average levels of Ca II H and K fluxes and an existing relationship of the decrease of Ca II fluxes with age on the lower main sequence and were drawn from previous results based on theoretical isochrone fitting. Values of the projected rotational velocity, v sin i, are determined for 70 Vir and 47 UMa from high-resolution spectra.

A SEARCH FOR OPTICAL FLARES IN CHROMOSPHERICALLY ACTIVE STARS

ABSTRACT We have surveyed four years of archival UBV photometry of 69 chromospherically active stars obtained with the Phoenix-10 automatic photoelectric telescope in search of optical flares on these stars. We demonstrate taht, while flares can be detected in these data, the number of events observed on evolved stars remains very small. Flares were found only on UX Arietis, II Pegasi, and AR Piscium.

Astronomy in South Africa

This note reviews those aspects of astronomy in South Africa that may be useful for the support of astronomical development on the rest of the African continent.Optical and infrared astronomy is largely consolidated at the Sutherland site of the South African Astronomical Observatory (SAAO), about 300 km from Cape Town. The administrative and technical headquarters of this institution occupy the buildings of the old Royal Observatory (founded in 1820) in Cape Town. In Cape Town there is a twin 18/24 inch (0.45/0.6m) refractor and an 18-inch (0.45m) photometric reflector still operational. At Sutherland the 74-inch (1.8m Radcliffe) reflector is equipped for spectroscopy, CCD imaging and IR photometry. Newtonian and coudé foci are available but rarely used. Also at Sutherland there are 40-inch, 30-inch and 20-inch telescopes (approx. 1m, 0.75m and 0.5m) used primarily for CCD imaging (40-inch), optical and infrared photometry (30-inch) and UVBRI standard photometry (20-inch). An automatic photoelectric telescope (30-inch aperture) is nearing completion. Observing conditions at Sutherland provide about 50% photometric time.

Optical variability in the unusual K5 V infrared-excess star HD 98800

The dusty infrared-excess star HD 98800 (K5 V) was observed for several weeks in the spring of 1993 by the Vanderbilt/Tennessee State 0.4 m automatic photoelectric telescope. It was found to be a variable star with an amplitude of 0.07 mag in V and a period of 14.7 days. We show, by comparison with other chromospherically active variable stars and constant stars with good observational histories, that the Rossby number for HD 98800, determined to be 0.30, places it well within the regime of stars whose convective envelopes and rotation rates combine to drive a magnetic dynamo strong enough to generate photometrically observable starspots. The light curve suggests at least two large spots at somewhat different longitudes on HD 98800, one of which could be as large as 16 deg in radius.

Photometry of Chemically Peculiar Stars with Automatic Photoelectric Telescopes

AbstractThe College of Charleston The Citadel, the University of Nevada, Las Vegas and Villanova University constitute the Four College Automatic Photoelectric Telescope Consortium which has a 0.75-m telescope on Mt. Hopkins, Arizona. It has been in regular operation for two years. Prior to this time we obtained some differential UBV observations with the Phoenix 10” APT of the Fairborn Observatory. We are coordinating observations of CP stars of the upper main sequence. Some initial results include evidence for significant changes in the light curve of 56 Ari, the constancy of the HgMn stars 53 Tau and HR 4072, an improved period for HD 244801, and new observations in the broad minimum of HD 9996.

Determination of Data Quality and Results from two Mount Hopkins Robotic Telescopes

AbstractWe present various methods for determining night quality from observations obtained with totally unattended automatic photoelectric telescopes at the Fairborn Observatory site on Mt. Hopkins, AZ. Telescopes are the Phoenix 10-inch (P10) and the Four College 75-cm (CAPT). Filter systems used are Johnson UBV, Kron-Cousins RI and Strömgren uvby. As a preliminary data filter for the P10 “rent-a-star” data, all observations with standard errors of the mean (SEM) above 20 mmag are discarded; a summary of nightly SEM’s, number of aborts and total observing time is sent to each user. The CAPT data are evaluated by standard deviation of magnitudes or counts for photometric groups and for an entire night. The Geneva photometric statistics are computed for these latter data and have proved useful as a preliminary screen for bad data. Various criteria for good and bad groups and nights are discussed. Scientific results are presented for several magnetic CP stars that were observed using both telescopes. Differences in precision of the data and strategies for observing are discussed.

A SEARCH FOR ECLIPSES IN (DELTA)SAGITTAE

ABSTRACT A photometric search for eclipses in Delta Sge, an M2 II + B7 V binary system, has been carried out with UBV data from the Automatic Photoelectric Telescope Service. None have been found, although at the predicted time of conjunction there was a small but significant decrease in (U - B). However, since this phase is one at which the M star is (nearly) in front of the B star it is unlikely that a bluer (U - B) could signal an atmospheric eclipse. Possibly it is due to heating induced by a reduced separation of the stars at periastron (e = 0.41), which occurs only about a month before conjunction. The M star was found to have dominant pulsation periods of about 40 and 24 days.

R CORONAE BOREALIS IN 1989

ABSTRACT A fourth annual report of UBV photometry of R CrB is presented, in this case covering 98 nights of Automatic Photoelectric Telescope observations in the 1989 season. Throughout this time the star was below its usual maximum brightness, but a three-month quasi-stationary interval reveals the usual low-amplitude (∼0.2 mag in V) pulsations with the single period 0f41d.1 1d.5 which is not significantly different from the customary 43d.8 value.

Photometry of 50 suspected variable stars

Fifty stars have been chosen as suspected variable stars and analyzed for variability. A large portion of this sample are stars that are either proved active chromosphere stars or are candidates for such activity. The photometric data base consists of differential V measurements of the Vanderbilt 16 inch (41 cm) automatic photoelectric telescope and 25 observers at 26 observatories worldwide. Published photometric data have also been utilized, with proper adjustments made to ensure that all magnitudes are differential. Searches for photometric period, amplitudes, and times of minimum light showed 68 percent of the sample to be photometrically variable with periods found for 34. Two stars were deemed norvariable for the period of observation. Conclusive statements could not be made concerning the photometric variability of the 14 remaining stars.

89 HERCULIS AND HD 161796 IN 1988

ABSTRACT New UBV photometry of V441 Herculis (89 Herculis) and 814 Herculis (HD 161796) obtained with the automatic photoelectric telescope service is presented. These two stars are members of a class of variable known as UU Herculis stars, high-latitude F supergiants that have curious properties. The intention behind the ongoing photometry is to obtain sufficient data with which to study the systematics of the variability of the stars.

U - B - V photometry of the spectroscopic-visual triple HD 165590

HD 165590 is a visual binary (dG0 + dG5,P = 20.y25,e = 0.96) whoseA component is an SB1 double (dG5 + dM:P = 0.d88,e≈0.0). TheA pair (Aa +Ab) undergoes partial eclipses. PhotoelectricUBV photometry from Lines and one of the Automatic Photoelectric Telescopes, andV photometry from Scarfe are examined here. The data are from the 1977, 1984, 1985, and 1986 observing seasons. The non-eclipse light variations are analyzed with a FORTRAN program which does a sinusoidal curve fitvia least squares repeatedly to obtain the best period. Periods found from each observing season and passband are consistent with Boydet al. (1985): the greatest variations seem to be produced by a rotating (∼0.d88), spotted, G0 star (theAa component). To the residuals from the first analysis a further curve fit is made to determine characteristics of the wave due to the ellipticity effect. An early limit on the spectral type of the unseenAb component, based on the primary eclpse depth and the upper limit on the depth of the unseen secondary eclipse, is K2. Eclipse depths and widths seen here suggest that theA pair's inclination = 74.09 ± 10, close to theA +B inclination of 82.07 ± 20 (Battenet al., 1979). TheA pair's orbital period does not appear to vary, appearing instead to be well-described by a new linear ephemeris (Hel. J.D. = 2443665.4568 + 0.d8795045E) which does, however, take into account a variable light-travel-times as theA component orbits theA +B center of mass with a 20.y25 period. The maximum light-travel-time O-C thus produced is + /−8.m4 = + /−0.d0059.

Automatic Photoelectric Telescopes focus on nighttime sky

Every clear night, three small telescopes atop Mount Hopkins, Ariz., swing into operation, make observations of designated stars and record the data. At dawn, the telescopes are stowed away. Remarkably, the entire observing session proceeds automatically, without any human intervention.

THE AUTOMATIC PHOTOELECTRIC TELESCOPE SERVICE.

ABSTRACT Automatic observatories have the potential of gathering sizable amounts of high-quality astronomical data at low cost. The Automatic Photoelectric Telescope Service (APT Service) has realized this potential and is routinely making photometric observations of a large number of variable stars. However, without observers to provide on-site monitoring, it was necessary to incorporate special quality checks into the operation of the APT Service at its multiple automatic telescope installation on Mount Hopkins.

Automatic photoelectric telescopes: status and potentials

Automatic photoelectric telescopes now exist. They are currently doing precision photometry of variable stars, fully automatically. More such telescopes will exist in the near future, and they will be doing automatic photometry of all sorts.

Variable star observations with automatic telescopes

Small automatic telescopes have been used for several years to make wide band, differential photometric observations of brighter variable stars. For example, a single automatic telescope located in Arizona has been used to study essentially the entire class of RS Canum Venaticorum binaries. These stars have changing spot structures that require once-a-night photometric observations - an ideal job for an automatic telescope located in the clear skies of Arizona. The operation of such automatic systems has become so routine that an “Automatic Photoelectric Telescope Service” now makes photometric observations for any institution so requesting. A list of stars is sent to the Arizona site of this service, and every three months the observational results are returned, with the cost typically being similar to the publication page charges. Currently the use of automatic telescopes is being extended to fainter stars and narrower bandwidths. For instance, a highly specialized one-meter telescope has been designed for automatic observations of Ca II K-line emissions from brighter active chromosphere stars. Further extensions of such automation seem likely.

REFLECTIONS ON THE SOLAR-STELLAR CONNECTION.

ABSTRACT The achievements of optical astronomy in the investigation of the sun as a typical star in connection with the study of stellar evolution are reviewed, with emphasis given to the accomplishments of George Ellery Hale. Consideration is given to the discovery of magnetic fields on the sun; measurements of temperatures in the solar corona; and the early history of observational techniques for high dispersion solar spectroscopy. The development of satellite based astronomical devices such as the IUE, the Einstein Observatory, and the Space Telescope, is also considered. The construction of automatic photoelectric telescopes (APTs) for observations of variable stars is also discussed.