Observing Campaign to Monitor Magnetically-Active Dwarfs for Long-Term Variability

From AAVSO Alert Notice 406:

The observers of the AAVSO are asked to participate in a long-term photometric monitoring campaign on a number of magnetically active dwarf stars, requested by Dr. Styliani (Stella) Kafka of the Department of Terrestrial Magnetism, Carnegie Institute of Washington. She requests long-term monitoring of these targets with an observing frequency of one observation every three days taken with one or more filters. When multiple filters are available, the preferred observations are (in order of precedence): Rc, V, Ic, and B. Please observe such that you obtain a signal to noise of at least 50 (100 or higher is preferred).

These objects are all nearby dwarfs known or suspected to have magnetic activity, primarily of the UV Ceti (flare star) or BY Draconis subtypes. Long-term photometric monitoring of these objects will be used in conjunction with other multiwavelength observations from ground-based facilities including the Magellan 6.5-meter and DuPont 2.5-meter telescopes in Chile to understand the long-term magnetic activity cycles of these stars. Such a study can reveal information about the physical natures of these stars, but also about their near space environments and habitability for life.

These objects are red, and the variability amplitudes are low, often well below 0.1 magnitudes. The long-term variability due to stellar activity cycles may be much lower. Photometric accuracy rather than the number of observations are key to the success of this project. Unaccounted-for atmospheric effects such as extinction will likely overwhelm any long-term signal from these stars. Observers are strongly urged to fully calibrate their systems and to carefully reduce and transform their photometry to standard photometric passbands, including corrections for airmass/atmospheric extinction.

Because of the long-term nature of this project, observers are asked to select one or more targets from the list below that are best suited to their system, and to add them to their observing schedules at a low priority. One observation every few days will be sufficient to trace the long-term behavior. Intensive time-series is not required, although observers may detect rapid, large-amplitude variations occurring in the flare stars; if you believe a flare is occurring during your exposure, please indicate this in the comments field when submitting data. Note that flares will have much larger amplitude at bluer wavelengths.

Please also note that the majority of these stars are high proper motion systems. Charts generated with AAVSO VSP may not accurately reflect the current positions of these objects. If you perform automated aperture photometry of your exposures, please verify that the object is in the expected position. We also request that you save your reduced frames for future analysis. We may request that you submit your frames to the AAVSO website or directly to Dr. Kafka at some point.

Please contact Matthew Templeton (matthewt at aavso.org) for AAVSO- or other observing-related questions, and Stella Kafka (stellakafka at gmail.com) for specific, project-related questions.

AAVSO participation in this project is important and your help will be greatly appreciated!

Observing Schedule

This is a very long-term campaign, with low-level but consistent observations requested over two years or more. Intensive time-series are not required.

We suggest that you select a small number of stars per season and concentrate on only those. A large number of observers individually making a small number of well-calibrated observations would easily fulfil the needs of this program. Select stars for a given observing quarter such that the target is at its highest elevation when performing photometry, preferably as close to transit as possible, to minimize extinction effects.

Photometric requirements

Calibration and extinction-correction of photometry is strongly encouraged; doing so enables us to combine data from multiple observers, and to eliminate spurious sources of variability like airmass effects. This is primarily an instrumental campaign in which calibrated observations taken in standard Johnson-Cousins filters are preferred. Filters requested in order of preference are: Cousins Rc, Johnson V, Cousins Ic, and Johnson B; other filters such as Sloan may be used if they are available. Note that because these targets are red stars, they will likely be brighter in Rc,Ic than in V, and much brighter than in B.

For a basic guide to system calibration and photometry, see the current version of the CCD Observing Manual. This manual is currently under revision, but will provide a basic overview of how to calibrate your system and apply this information to your photometry. For questions, please contact Arne Henden (arne at aavso.org), Matthew Templeton (matthewt at aavso.org), or post a question to the AAVSO-Photometry Mailing List. There will also be a one-hour presentation on calibration and transformation of photometry by Dr. Arne Henden at the AAVSO Annual Meeting on November 5-7, 2009. Attendees of the meeting are encouraged to attend this important lecture.

Target List

Observations of the following stars are requested as part of this campaign: