Title: "A Study and the Period and Amplitude Behavior of BL Her and RR1 stars
in the Metal-Poor Globular Cluster M56 in Lyra"
Proposer: Doug Welch
I propose to obtain V and I images of the globular cluster
M56 in Lyra in order to study the possible period and
amplitude modulation of the BL Her star V1 (P=1.51 days, <R>=15.10)
and RR1 stars V4 (P=0.424 days, <R>=15.75) and V14 (P=0.381 days, <R>=15.69).
The two published studies of M56's variable stars in recent times
are by Horne (2005) and Pietrukowicz et al (2008). Horne's 10cm telescope
and (now) small-format CCD camera produced a useful time of maximum for V1,
but for the fainter RR1 stars, it was a "bridge too far". The paper was more
of a demonstration project than a reporting of useful photometry.
Reasons for extending the observations of Pietrukowicz et al (2008)
- their photometry was the only digital photometry yet published,
but it was made unfiiltered.
- typical seeing was relatively poor (FWHM=4.5 arcsec).
- observations were taken over a two-year period (Jul 2002-May 2004).
and period change (noted for V1) and the nature of the period
change can be facilitated by more recent digital data.
- Both V4 and V14 show sufficient "noise" in their lightcurve to
study the degree to which they resemble the RR1 sample characterized
by Welch and Foster (2013).
- the cluster is exceedingly well-placed for northern hemisphere
Cluster center: 19:16:35.57 +30:11:00.5 (J2000.0)
Proposed telescope: One of SRO or TMO61 (TMO61's larger aperture.
finer image scale, and better possible image quality probably outweighs
SRO's longer continuous summer observing season).
Cadence: Nightly observations requested except during the interval when
observations separated by four hours or more are possible
at airmasses lower than 1.6.
Duration: 2014, 2015, and 2016 observing seasons
Reduction: Daophot/Allstar/Allframe necessary because of the crowding
of some of the targets.
Horne, J.D. 2005, JAAVSO, 34, 61.
Pietrukowicz, P. et al 2008, Acta Astronomica, 58, 121-130
"CURious Variables Experiment (CURVE): Variable Stars in the
Metal-Poor Globular Cluster M56"
Welch, D.L. 2012 "Type 2 Cepheids in the Milky Way Galaxy and the Magellanic Clouds"
JAAVSO, 40, 492. http://www.aavso.org/sites/default/files/jaavso/v40n1/492.pdf
Welch, D.L. and Foster, G. 2013
"A Study of RR1 Lightcurve Modulation in OGLE_III Bulge Time-series"
Presented at the "40 Years of Variable Stars: A Celebration of Contributions by Horace A. Smith"
conference. 11 pages, 12 figures
Current major use of AAVSOnet resources:
I have an on-going program with Ken Mogul to acquire photometry on three dozen field Type 2 Cepheids
to assess what evidence might exist for binarity in their lightcurves (combined with +/-2 km/s
radial velocities of the brighter objects from the DAO 1.2m telescope). Originally on K28,
the continuity of this program was interrupted by the decision of T. Kracji to suspend data-taking
and then many-month gaps between new data from W30 and then its successor Coker30. The program
is still underway, but will require at least one more year of data acquisition on Coker30 to
complete the original science goals. Since the data were taken in Sloan griz, calibration
and reduction is most efficient once APASS DR8 is available within VPHOT. Sloan standards
are available in VPHOT at present.