Band 12, Heft 2

TRIPP is an aperture photometry program designed with the purpose of extracting light curves from large sets of similar CCD frames typically obtained during time-resolved photometric monitoring campaigns such as, for example, WET runs. We describe its properties and usage with an emphasis on where the functionality of TRIPP may differ from similar programs, and try to outline both its strengths as well as the non-trivial issues where difficulties may arise.

For many years, the Whole Earth Telescope has used the QED software package, created by R. E. Nather, to reduce the data gathered from the WET standard, PMT based photometers. While essential for reducing this data, QED alone is not a sufficient package for reducing CCD photometry data, which is becoming a larger fraction of WET data. In addition, QED requires DOS, while many astronomers, and WET HQ, do everything in a different environment (usually Unix based). A new version of the data reduction software will allow the WET to continue to operate with future CCD photometers and systems, and to reduce archival photometry data with new computer systems. Here a software package is described which will satisfy these new needs.

As the WET moves to CCD systems, we move away from the uniformity of the standard WET photometer into an arena where each system can be radically different. There are many possible CCD photometry systems that can fulfil the requirements of a WET instrument, but each of these will have their own unique native data format. During XCov22, it became readily apparent that the WET requires a defined data format for all CCD data that arrives at HQ. This paper describes the proposed format for the next generation of WET data; the final version will be the default format for XQED, the new photometry package discussed elsewhere in these proceedings.

A brief summary of the improvements recently made by the Vilnius WET group to Tromsø CCD photometer for time resolved photometry is provided.

The goal of the WET collaboration is to produce a photometric light curve as continuous and accurate as possible, given the weather and technical constraints. In order to join light curves from different observers, it is important that all observer’s clocks are accurately synchronised with Universal Time, and with a precision substantially better than one second. This requires vigilance and careful checking by the observer, who needs to be familiar with the instrument and how the integration intervals are determined. This is in particular important with the introduction of the more complex CCD photometers. Ideally each observer should have access to their own time source, and a GPS solution is recommended. It is also important that the information about timing peculiarities are carefully checked and recorded and passed on to the data analysts.

Account of the extinction in the Earth’s atmosphere is an important part of the WET light curve reduction procedures. Usually, WET observations are not corrected for the second order extinction effects: the dependence of the extinction coefficient on spectral type and on air mass (the Forbes effect). The ignorance of these effects does not change seriously the derived pulsation amplitudes at the frequencies higher than 200 μHz but the increase of the noise at lower frequencies takes place. For obtaining the true extra-atmospheric magnitudes of stars, a modification of the extinction correction procedure is proposed. For photometry with the R647 phototube we recommend to use a filter cutting out the region below 310 nm, in order to decrease and stabilize the extinction coefficient. A method for estimation of spectral type of the comparison star from WET observations is proposed.

The multiple object and multiple frame (MOMF) CCD photometry package, that combines the advantages of aperture and PSF photometry is described. Results from comparisons with other programs are given; no other photometry package was found to give better results than MOMF.

A recent re-analysis of Whole Earth Telescope observations of GD 358 obtained in 1990 suggest that asteroseismology of additional DBV white dwarfs can lead to independent constraints on the important, but poorly determined, 12 C(α, γ) 16 O nuclear reaction rate. Data exist for several other DBV white dwarfs, but relatively few modes are detected and there is often no multiplet structure to aid in the identification of the spherical harmonic indices l,m. I use a new grid of one million DBV models covering a broad range of masses, temperatures, and surface helium layer masses to investigate the consequences of assuming m=0 for global model-fitting. I find that when the spherical degree is known and the rotation period is of order 1 day, the model-fitting procedure applied to modes with unknown m values will still correctly identify the families of possible solutions, and has a high probability of identifying the same globally optimal solution found when the m-value is known.

I have investigated the value of the contribution of small telescopes to the success of a whole WET run. To this end, I have applied different data weighting schemes to two extreme WET test data sets. I find that weights proportional to the inverse local scatter in the light curves produce Fourier Transforms of best signal-to-noise. Weighting data stronger than their inverse scatter does not yield optimal results because of the reduction of the effective number of data points. The contribution of the small telescopes to the combined WET results was found to be very important. They do not only improve the spectral window, but they can reduce the noise in the total FT by more than their light gathering power would imply. Some suggestions for the optimal use of small telescopes in the WET are given.

The Whole Earth Telescope collaboration is build solidly on the interest of the participants. One of the goals of the collaboration is to produce a high signal to noise, as continuous as possible, light curve for a selected target. During the nearly 15 years of existence the operation of the network has been based on what the members have been able to provide of local funds for their own participation, in addition to NSF grants to run the headquarters activities. This has led to a very uneven geographical distribution of participating groups and observatories. An analysis of the coverage of some of the last WET runs shows that we still have large holes in the coverage, and this leads to aliasing and loss of precision in our final products.

The Mt. Dushak-Erekdag Observatory (Central Asia, Turkmenistan, 58° E longitude) is located just in the longitudes gap of asteroseismological networks. It is the southernmost observatory of the former Soviet Union, its latitude is +38°. The sky seeing at the site is one of the best in Central Asia: a low light pollution, high and stable sky transparency, over 200 usable nights per year. The altitude is above 2000 m. Odessa Astronomical Observatory has its 0.8 m telescope with a two-star high-speed photometer there, which frequently participates in international programs and multi-site campaigns. An accuracy of the photometry amounts to 1 mmag. Besides, a 1 m wide-angle telescope and a dual-tube telescope with 0.5m mirrors are installed at the observatory. The developed infrastructure at the site and the stable economy in Turkmenistan make the Mt. Dushak-Erekdag Observatory very interesting for the WET observations.

We present analysis of the data collected during three years of photometric campaigns at the 91 cm Cassegrain telescope of the Catania Astrophysical Observatory to observe the pulsating subdwarf B star PG 1336-018. For this eclipsing binary system, we obtained a precise determination of the orbital period which turns out to be P = 0.10101599±0.00000002 days. Time-series photometry reveals pulsation periods near 174 and 184 seconds. We also discuss a preliminary analysis of the data obtained in 2002 for the pulsating subdwarf PG 1325+101.

White Dwarf Research Corporation is a non-profit organization dedicated to scientific research and public education on topics relevant to white dwarf stars. It was founded in 1999 in Austin, Texas to help fulfill the need for an alternative research center where scarce funding dollars could be used more efficiently, and to provide a direct link between astronomers who study white dwarf stars and the general public. Due to its administrative simplicity, WDRC can facilitate the funding of multi-institutional and international collaborations, provide seamless grant portability, minimize overhead rates, and actively seek non-governmental funding sources. I describe the motivation for, and current status of, one of the long-term goals of WDRC: to establish a permanent endowment for the operation of the Whole Earth Telescope. I pay particular attention to fund-raising efforts through the website at http://WhiteDwarf.org/donate/.