J/AJ/154/217 Period variations for the Cepheid VZ Cyg (Sirorattanakul+, 2017)
Period variations for the Cepheid VZ Cyg.
Sirorattanakul K., Engle S., Pepper J., Wells M., Laney C.D.,
Rodriguez J.E., Stassun K.G.
<Astron. J., 154, 217 (2017)>
=2017AJ....154..217S 2017AJ....154..217S (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Photometry, UBV
Keywords: stars: variables: Cepheids
Abstract:
The Cepheid Period-Luminosity law is a key rung on the extragalactic
distance ladder. However, numerous Cepheids are known to undergo
period variations. Monitoring, refining, and understanding these
period variations allows us to better determine the parameters of the
Cepheids themselves and of the instability strip in which they reside,
and to test models of stellar evolution. VZ Cyg, a classical Cepheid
pulsating at ∼4.864 days, has been observed for over 100 years.
Combining data from literature observations, the Kilodegree Extremely
Little Telescope (KELT) transit survey, and new targeted observations
with the Robotically Controlled Telescope (RCT) at Kitt Peak, we find
a period change rate of dP/dt=-0.0642±0.0018 s/yr. However, when
only the recent observations are examined, we find a much higher period
change rate of dP/dt=-0.0923±0.0110 s/yr. This higher rate could be
due to an apparent long-term (P∼26.5 years) cyclic period variation.
The possible interpretations of this single Cepheid's complex period
variations underscore both the need to regularly monitor pulsating
variables and the important benefits that photometric surveys such as
KELT can have on the field. Further monitoring of this interesting
example of Cepheid variability is recommended to confirm and better
understand the possible cyclic period variations. Further, Cepheid
timing analyses are necessary to fully understand their current
behaviors and parameters, as well as their evolutionary histories.
Description:
KELT is a photometric survey using two small-aperture (42 mm) wide-field
robotic telescopes, KELT-North at Winer Observatory in Arizona in the
United States (Pepper et al. 2007PASP..119..923P 2007PASP..119..923P), and KELT-South at
the South African Astronomical Observatory near Sutherland, South Africa
(Pepper et al. 2012PASP..124..230P 2012PASP..124..230P). VZ Cyg is located in KELT-North
field 12, which is centered at J2000 α=21.4h, δ=+31.7°.
Field 12 was monitored for seven seasons from UT 2007 June 08 to UT
2013 June 14, acquiring a total of 5159 images after post-processing
and removal of bad images.
Recent CCD BV photometry of VZ Cyg (see Table 3 and Figure 1) were also
carried out for this program with the 1.3 m Robotically Controlled
Telescope (RCT; Strolger et al. 2014AJ....147...49S 2014AJ....147...49S) at Kitt Peak National
Observatory (KPNO). Two seasons were obtained: Season 1 from 2015 August 15
to December 14 and Season 2 began on 2016 August 20 to November 19.
Objects:
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RA (ICRS) DE Designation(s)
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21 51 41.44 +43 08 02.5 VZ Cyg = V* VZ Cyg
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 27 5159 KELT Photometry of VZ Cyg
table3.dat 31 252 RCT BV Photometry of VZ Cyg
table4.dat 107 60 O-C Data for VZ Cyg
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See also:
J/A+A/404/423 : BVI photometry of Galactic Cepheids (Tammann+, 2003)
J/PAZh/39/942 : Galactic classical Cepheids properties (Marsakov+, 2013)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d HJD Heliocentric Julian Date
16- 21 F6.3 mag KELTmag [-0.493/1.335] Relative KELT instrument
magnitude
23- 27 F5.3 mag e_KELTmag [0.001/0.016] Formal error in KELTmag
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 1 A1 --- Filt [BV] Filter used
3- 16 F14.6 d HJD Heliocentric Julian Date
18- 24 F7.4 mag mag [8.6067/10.2972] Apparent RCT magnitude in Filt
26- 31 F6.4 mag e_mag [0.0003/0.0414] Formal error in mag
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 12 F12.4 d Tmax Time of maximum light (HJD)
14- 18 I5 d Epoch [-4333/3281] Epoch of the observation
20- 26 F7.4 d O-C [-0.4421/0.0418] O-C for Epoch
28 I1 --- Weight [1/3] Weight
30- 35 F6.4 d e_O-C [0.0025/0.1458]? Uncertainty in O-C
37- 56 A20 --- Ref Reference
58-107 A50 --- Bibcode Bibcode of the reference or comment
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 07-Aug-2018