Alert Notice 789: Photometry and spectroscopy requested for 9 TESS targets

August 22, 2022

AAVSO Forum threads (scroll to the bottom of a thread for latest posts):
- Campaigns and Observing Reports: https://www.aavso.org/flare-stars-tess-campaign-2022-2023

Please subscribe to these threads if you are participating in the campaign so you can be updated by the astronomers and by HQ. Join in the discussion or ask questions there!

AAVSO member Robert Buchheim, on behalf of Dr. James Jackman (Arizona State University) and himself, have requested AAVSO observers' assistance in a campaign underway on flare stars.

Buchheim provides the following information: "We request time-series photometry and spectroscopy of nine M-dwarf flare stars, starting now and continuing through January 18th, 2023.  The ground-based photometry and spectroscopy will be combined with TESS photometry, to characterize the stellar flares.  Coordinated multi-wavelength photometry and spectroscopy will improve our understanding of flare contribution to the high energy environments of low-mass stars.

The target stars, and the schedule for TESS observations are:

These are all red dwarf stars, V-mag between 8.5 and 11.2.

TESS will provide continuous high-accuracy time-series broad-band photometry at 20-sec cadence during the indicated observation windows for each of these stars.  The goal for AAVSO observers is to provide time-series photometry in B- and V-band and time-series spectroscopy throughout the observation window for each star.  Based on previous flare-star campaigns, the following guidance is offered:

Photometry:  For continuous time-series photometry, it is best if each telescope is devoted to a single filter (Johnson-Cousins B- or V-band), rather than cycling the filter wheel.  Flares that we have detected in previous campaigns are stronger in B-band, but we also need V-band for two reasons:  (a) to provide flare color information, and (b) to facilitate flux-calibration of simultaneous spectroscopy when it available. These bands are preferred to DSLR blue and green. CV observations are not appropriate for analysis for this campaign.

The typical flare signature is a rapid rise and gradual decay in brightness, with the “rise” phase lasting between zero and a few minutes, and the decay phase lasting from a several minutes to an hour.  Flares that we have previously detected in B- and V-band ranged from as little as 0.05 mag, to as much as 2 magnitudes.  Observing cadence is driven by the need for good SNR and for good time resolution.   The desired photometric SNR is ≥50 (sufficient for photometric accuracy better than 0.03 mag).  Set your exposure time based on SNR, and take images continuously, with no delay between exposures.  Long observing runs are needed – ideally, someone will be observing all night every night during the observing window.

If you are using multiple telescopes, then devoting one to B-band and the other to V-band will be valuable.

Photometry results should be submitted to AAVSO via WebObs.

Low-Medium Resolution Spectroscopy:  Continuous time-series spectroscopy at R≈ 500 – 2000, covering the optical band is requested (e.g. Shelyak ALPY, LISA, UVEX spectrographs).  The flare signature in spectroscopy is a rapid rise in Balmer emission lines, sometimes accompanies by a rise in the continuum at the blue end of the spectrum (below about 4500Å) and by other emission lines.  Time-series spectra at a cadence of 2-5 minutes per image, continuously for all night if practical, is requested.  Calibration Lamp image (for wavelength calibration) should be made at the start and end of each observing session; a Reference Star (for Instrument+atmospheric Response correction) should also be observed, ideally at the beginning, middle, and end of each night’s session.

Process your spectra into 1-D FITS files, wavelength-calibrated and response-corrected; one spectrum per image (ISIS has a convenient method to do this).  We are setting up an on-line location where you can upload your nightly time-series spectra.  Contact Bob Buchheim (oca_bob@yahoo.com) for details.

We have not experimented with slitless spectroscopy for flare star observations, but it might be useful: process and submit your data in the same way as described above.

High-Resolution Spectroscopy:  Time-series spectroscopy at R≈ 5000 or greater (e.g. Shelyak Lhires) might be able to measure emission-line profile changes during large flares.  Observing cadence will probably be 5-minute exposures, continuously each night, with appropriate Calibration Lamps (wavelength calibration) at the beginning and end of each observing run.

Process your spectra into 1-D FITS files, wavelength-calibrated and response-corrected; one spectrum per image (ISIS has a convenient method to do this).  We are setting up a Google Drive location where you can upload your nightly time-series spectra.  Contact Bob Buchheim (oca_bob@yahoo.com) for details.

Acknowledgements:  All observers who provide data will be recognized in some way.  Observers who make a significant contribution through their data will be considered for coauthorship on resulting papers.

Background information:  You can learn about our previous flare-star photometry+spectroscopy results in the SAS-2022 Proceedings (https://socastrosci.org/wp-content/uploads/2022/05/2022_Proceedings.pdf); see the papers by Sims et al. (p. 139), Buchheim et al. (p. 151), and Boyd et al. (p. 160).

Videos of relevant presentations are available at:

  - Sims et al.:  https://www.youtube.com/watch?v=XO2Pys1hv5s&list=PLmQ5Bvz4ACYISWNChWPwzPHMPkK5cVcZd&index=23

  - Buchheim et al.:  https://www.youtube.com/watch?v=NUTrKSCasZI&list=PLmQ5Bvz4ACYISWNChWPwzPHMPkK5cVcZd&index=24&t=2s

  - Boyd et al.:  https://www.youtube.com/watch?v=Zm5jWDRvzEg&list=PLmQ5Bvz4ACYISWNChWPwzPHMPkK5cVcZd&index=25

  - Jackman:  https://www.youtube.com/watch?v=r_aj5IfongU&list=PLmQ5Bvz4ACYISWNChWPwzPHMPkK5cVcZd&index=26

An edited version of the TESS proposal can be downloaded from https://www.dropbox.com/s/zwobxm4jhmwyw3t/Cycle%205%20proposal.pdf?dl=0

Coordination:  We will have bi-weekly Zoom meetings to discuss observing and processing details, interim progress, coordination of observing schedules, and questions.  If you would like to be invited to these meetings, contact Bob Buchheim at <oca_bob@yahoo.com>.

Note: EQ Peg A has a very close companion - EQ Peg B, ≈mag 12.4, about 5 arc-sec from EQ Peg A (per Washington Double star catalog measurement in 2020). If your observation includes this companion, when you submit observations, please include a comment/note that you are reporting photometry or spectra that includes both stars."

Finder charts with comparison stars for the targets may be created using the AAVSO Variable Star Plotter (VSP). The targets are signficantly high-proper-motion stars, so they will not be at the exact position plotted on the chart. Comparison stars for some of the targets are being selected as this Alert Notice goes to press. If there are no comparison stars on the plot you create, please check again later. Hold on to your images so you can reduce them when the comparison stars are available.

Please submit your observations to the AAVSO International Database and/or the AAVSO Spectroscopy Database (links below) using the names in the table.

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen using material provided by Robert Buchheim.

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SUBMIT OBSERVATIONS TO THE AAVSO

Information on submitting observations to the AAVSO may be found at:
 - Photometry/visual observations: https://www.aavso.org/webobs
 - Spectroscopy: https://www.aavso.org/apps/avspec/

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