Proposal #75

Proposer: Mike Nicholas – nmi
mnicholas5cox@gmail.com

Campaign 4 of the Kepler K2 Mission has observed the Pleiades for the development of “Halo” photometry. This new technique allows professional class telescopes to photometrically measure bright stars by avoiding the saturated center pixels and only measuring the nearby unsaturated pixels in the image. A recent paper (https://arxiv.org/pdf/1708.07462.pdf) discusses this technique as it was applied to the study of these B stars in Taurus. One hope for this tool is its application for follow-up Kepler missions and for future space telescopes such as the Transiting Exoplanet Survey Satellite (TESS).

This proposal suggests there is value in (1) having BSM precision photometric “unsaturated” data and image sets to support “Halo” photometry development and (2) for follow-up observations of the these blue pulsators. It should be noted that the afore-mentioned paper suggests that Maia variability (10 day) may be caused by rotational modulation resulting from a large chemical spot. Alcyone (NSV 15775) is the only target that does not have an AUID. These stars should be in reach of the Northern Hemisphere sites including Hamren, although I am unclear about the horizon limitations of the BSM stations.

Name RA (2000) Dec (2000) AUID # Magnitude *Freq. d^−1
Electra 03 44 52.50 +24 06 48.0 000-BCY-974 3.7 -? V >0.8
Taygeta 03 45 12.49 +24 28 02.2 000-BBG-197 4.29 V >0.4
Maia 03 45 49.61 +24 22 03.9 000-BBG-202 3.87 V >0.09
Merope 03 46 19.57 +23 56 54.1 000-BBG-219 4.18 (0.01) V >0.9
Alcyone 03 47 29.10 +24 06 18.0 (NSV 15775) 2.87 -? V >0.1
Atlas 03 49 09.74 +24 03 12.3 000-BBG-271 3.60 - 3.65 V >0.4
Pleione 03 49 11.22 +24 08 12.2 000-BBG-273 4.83 - 5.38 V >0.3
*https://arxiv.org/pdf/1708.07462.pdf, Table A1 through A7

There are AAVSO comparison stars with B and V data in this field, although dimmer than the targets. The AAVSO database contains some visual observations

It would seem appropriate to initially take twenty 0.5 second exposures for V and twenty 1.0 second exposures for B magnitudes to beat down scintillation and to determine SNR. It may also be useful to record low resolution spectra during each sequence. A single BSM image could capture all targets and comparison stars. Images would be send to VPHOT and personally archived.

Given that the paper suggests variability of less than one day, it seems appropriate to have more than one BSM station making observations. Observations could start as soon as possible and extend for the remainder of the observational season. If coordination with the professional community is useful that might be accommodated.

Other references:
http://harvard.voxcharta.org/tag/halo-photometry/
https://github.com/hvidy/halophot.