ASAS-SN V-band Light Curve of Multi-Planet M-dwarf Host YZ Cet Reveals a Rotation Period of 68 Days
ATel #10643; T. Jayasinghe, K. Z. Stanek, C. S. Kochanek, T. W.-S. Holoien, J. V. Shields, T. A. Thompson (OSU), B. J. Shappee (Hubble Fellow, Carnegie Observatories), J. L. Prieto (Diego Portales; MAS), Subo Dong (KIAA-PKU)
on 15 Aug 2017; 16:02 UT
Credential Certification: Krzysztof Stanek (stanek.32@osu.edu)
Subjects: Optical, Planet, Variables
Referred to by ATel #: 10678
The ASAS-SN project (Shappee et al. 2014; Kochanek et al. 2017)
provides all-sky, high-cadence variability data for objects with
V-band magnitudes between ~8 and ~17. In a recent paper,
Astudillo-Defru et al. (2017) studied a nearby (3.6pc) M-dwarf YZ Cet, which contains a system of (at least) three Earth-mass
planets, and reported a very long rotation period for the planet host
(~83 days). Data from the ASAS project (Pojmanski 1997) acquired between
2000 to 2009 were used in their analysis. Here we provide a contemporary,
well sampled ASAS-SN V-band light curve for that star.
YZ Cet has a high RA/Dec proper motion of ~1.4 arcsec/yr (van Leeuwen
2007), and therefore moves considerably even in large-pixel ASAS-SN
images (coordinates of YZ-Cet changed by ~7" over a 4-year period in
our data). We retrieved an ASAS-SN light curve, allowing for that
large proper motion, yielding
this light curve of 854 V-band photometric measurements obtained
between August 2013 and August 2017. A periodic signal, most likely
due to rotational modulation, is clearly present in 366 measurements
made after May 2016 (middle panel). An analysis of variance (AOV) periodogram shows a
stellar rotation period of ~68.3 days, significantly shorter than
~83 days reported by Astudillo-Defru et al. (2017). There is no evidence for the
83 days period in ASAS-SN data. We also derive the best
AoV period using the entire ASAS-SN light curve, which yields the same value of
P=68.3 days. The phased light curve is shown in the bottom panel
of this figure.
ASAS-SN light curve of YZ Cet is available upon request.
We thank Las Cumbres Observatory and its staff for their continued
support of ASAS-SN. ASAS-SN is funded in part by the Gordon and Betty
Moore Foundation through grant GBMF5490 to the Ohio State University,
NSF grant AST-1515927, the Mt. Cuba Astronomical Foundation, the
Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, and the
Chinese Academy of Sciences South America Center for Astronomy
