| Proposal | Good morning, I'm Sauro Gaudenzi, my observer code is GSAD. In support of AAVSO alert no. 892, I kindly request the use of a telescope to observe the object ZZ Psc (G29-38). I request a weekly observation of 60 60-second exposures with a V-filter. I request that observations begin immediately and run through December 31, 2025. Abstract:
Steven Savery (U. Delaware) writes: We request AAVSO optical photometry to provide simultaneous coverage and support a Whole Earth Telescope (WET) campaign to observe the pulsating white dwarf ZZ Psc (G29-38). These observations are part of an international multi-wavelength campaign to study G29-38 and its inner debris disk. The goal is to harness G29-38's photospheric pulsations observed at optical wavelengths to probe the disk morphology. The WET run is a coordinated effort to combine V band photometry from observatories spread out in longitude to create a well sampled light curve with minimum coverage gaps. The AAVSO photometry will provide an important component of this effort. The scientific goal is to compare concurrent optical photometry detailing G29-38's g-mode pulsation frequencies, amplitudes, and phases with the infrared frequencies, amplitudes, and phases to probe the composition and distribution of G29-38's debris disk. *SEE 'Additional Observer Input' FOR INSTRUCTIONS.* Justification:
We are requesting time-resolved photometric observations from AAVSO members as part of an international campaign to study the hydrogen atmosphere pulsating (DAV) white dwarf (WD) G29-38 and its debris disk concurrently in both optical and infrared wavelengths. For AAVSO observers, this project relies on differential photometry and does not require strict photometric conditions to observe. That means the telescope field-of-views (FOVs) need to be large enough to include the needed comparison stars. For G29-38, a FOV with a radius of approximately 5 arcminutes will be large enough. A smaller FOV may be usable, it would just require centering the image away from G29-38. AAVSO members will also provide important coverage of the secondary targets of this campaign when there are overlapping observations from telescopes at similar longitudes. We are planning to start optical observations a week before the scheduled infrared observations as G29-38's frequency distribution is known to change on the order of months (Kleinman et al. 1998). The scientific exposures should be between 10 and 30 seconds, to adequately sample the pulsations. The main observational campaign will span October 13 to 27. We request that these observations are taken using a V band filter, as G29-38 has a magnitude of 13.05 in this band, and while G29-38 is above 30 degrees in the sky. The goal is to investigate the disk's response to G29-38's photospheric pulsations and use that information to probe the disk morphology. These debris disks are important to our understanding of exoplanet composition and planetary system evolution, as they are thought to arise from disrupted planetary bodies (Reach et al. 2009). Understanding the nature of the dust in the debris disk and the geometry of its distribution is vital to calculate debris masses and lifetimes, and to constrain the mechanisms that resulted in the disk formation in the first place. G29-38 provides the perfect target to validate a new methodology to probe the morphology of WD debris disks. Recent work by von Hippel et al. (2024) served as proof of concept for this concurrent optical and infrared photometry campaign design. The work analyzes simultaneous optical (0.5 μm) and near-infrared (0.7-2.5 μm) time-series photometry obtained over a 2-day span. The authors use the 0.5-µm light curve, dominated by the WD's flux, to determine the frequencies, amplitudes, and phases of the photospheric stellar pulsations. The infrared light curves contain significant flux from the disk, and are used to detect variations in frequency, amplitude, and phase as a function of wavelength (von Hippel et al. 2024). The authors were able to identify flux variations at all wavelengths. The three stellar oscillations detected at 0.5 μm decrease in amplitude with increasing wavelength, as expected for WD g-mode pulsations (Graham et al. 1990). Unexpectedly, two frequencies that correspond to numerical combinations of the three previously mentioned WD g-mode oscillations were observed increasing in amplitude for wavelengths beyond 1.5 μm (von Hippel et al. 2024). The authors find no theoretical justification for these combination frequencies to increase in amplitude at infrared wavelengths (Wu 2001). In addition, the authors detected a significant phase change between the optical and infrared light curves for the largest amplitude stellar pulsations. Unfortunately, precise interpretation of these observations in terms of the disk's detailed morphology is limited by poor infrared coverage in von Hippel et al. (2024) which causes extensive aliasing and low signal-to-noise (S/N). Optical observations from AAVSO members will provide important longitudinal coverage, ensuring the needed campaign time base and limiting the gaps in observations. These observations will be compared to the infrared observations to determine how pulsation frequency, amplitude, and phase change with increasing wavelength, allowing us to probe the morphology of G29-38's debris disk. The Whole Earth Telescope (WET) is a network of telescopes spread across the Earth in longitude that are operated as a single instrument to obtain nearly continuous photometric observations of each target. Twenty to twenty-five telescopes typically participate in a single WET run. An interactive headquarters will communicate with observers nightly to ensure coverage of the primary target (G29-38). This coverage is crucial to accurately identify pulsations and multiplets seen in multiperiodic pulsators, as it prevents confusing window aliases in the Fourier analysis of the light curves. By merging data from individual sites into a single light curve, we acquire a nearly continuous time-series record of a star's brightness variations. When the run is complete, and the individual light curves merged, our data set with an expected time base of 14 days (1,200,000 seconds) will be able to identify frequency separations greater than 0.8 μHz. |
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