J/A+A/544/A28 Period variation in BW Vulpeculae redux (Odell, 2012)
Period variation in BW Vulpeculae redux.
Odell A.
<Astron. Astrophys. 544, A28 (2012)>
=2012A&A...544A..28O 2012A&A...544A..28O
ADC_Keywords: Stars, variable ; Photometry, UBV ; Photometry, uvby
Keywords: stars: evolution - stars: oscillations - Stars: individual: BW Vul
Abstract:
For the past 25 years, BW Vulpeculae has been the topic of period
analyses centered on a secular period change with a periodic variation
superposed, presumed to be due to light time effects in a binary
system. According to this paradigm, one would expect what seems like a
period increase of about 0.5s during or soon after the year 2001. I
have continued photometric monitoring through the year 2012, adding 40
new timings of maximum and minimum light. This expected change in
period did not occur, which rules out that interpretation of the
period variation. As of 2012, the observed timings are about two hours
early compared to those predicted by the quadratic ephemeris, but are
very close to those predicted by the linear ephemeris. In fact, the
period has remained constant for the last 32 years, indicating that
the previous epochs of constant period are almost certainly the
correct interpretation, though the cause of the period changes is
still not clear. Continued photometric monitoring of BW Vul leads to
the conclusion that the period changes are abrupt, followed by epochs
of constant period lasting between 12 and at least 32 years.
Description:
Photoelectric and CCD photometry were done between 1980 and 2012 with
a variety of telescopes and filter sets; the results are tabulated
here. The first file is data utilizing Stromgren filters (b and y
only), sometimes in a single-channel photoelectric photometer on the
Lowell 31" telescope or the 21" telescope, but one night with a CCD
camera on the 31" (JD 2452948). The second file contains data taken
with a photometer or polarimeter on various telescopes at University
of Arizona and Lowell Observatory; the filters used depends on the
night, but could be U, B, and/or V. The final file is data taken with
a CCD at the Lowell 31" and filters originally intended for continuum
measurements of comets; blue is 4450/67Å (central, FWHM
wavelengths), green is 5260/56Å, and red is 7128/58Å. These
non-standard filters were chosen to provide reasonable exposures for
the CCD without saturation or shutter pattern, yet the data is of the
highest quality of any set. The comparison star was SAO70596
(= HD198820 = HR7996); magnitudes are (Variable - Comparison); check
stars were not used. All phases in all tables were calculated with a
simple linear ephemeris that fits timings between 1980 and 2012:
HJD(max)=2444401.5916+0.201044004E; this is meant to be indicative,
but not necessarily reliable.
Objects:
-------------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------------
20 54 22.40 +28 31 19.2 BW Vul = V* BW Vul
20 52 00.39 +32 50 56.0 HR 7996 = HD 198820
-------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
stromgrn.dat 49 1520 Differential magnitudes (BW Vul - HR 7996) in
Stromgren b and y filters
johnson.dat 76 3598 Differential magnitudes (BW Vul - HR 7996) in
Johnson V, B, and U filters (not all are
included on each night)
comet.dat 74 275 Differential magnitudes (BW Vul - HR 7996) in
three comet continuum filters
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Byte-by-byte Description of file: stromgrn.dat
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Bytes Format Units Label Explanations
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1- 12 F12.4 d HJDb ? Heliocentric Julian Day for b band
14- 18 F5.3 --- Phaseb ? Phase for b band (G1)
20- 24 F5.3 mag Dbmag ? Differential Stromgren b magnitude
26- 37 F12.4 d HJDy ? Heliocentric Julian Day for y band
39- 43 F5.3 --- Phasey ? Phase for y band (G1)
45- 49 F5.3 mag Dymag ? Differential Stromgren y magnitude
--------------------------------------------------------------------------------
Byte-by-byte Description of file: johnson.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 F12.4 d HJDV ? Heliocentric Julian Day for V band
14- 18 F5.3 --- PhaseV ? Phase for V band (G1)
20- 24 F5.3 mag DVmag ? Differential Johnson V magnitude
26- 37 F12.4 d HJDB ? Heliocentric Julian Day for B band
39- 43 F5.3 --- PhaseB ? Phase for B band (G1)
45- 50 F6.3 mag DBmag ? Differential Johnson B magnitude
52- 63 F12.4 d HJDU ? Heliocentric Julian Day for U band
65- 69 F5.3 --- PhaseU ? Phase for U band (G1)
71- 76 F6.3 mag DUmag ? Differential Johnson U magnitude
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Byte-by-byte Description of file: comet.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 F12.4 d HJDbc ? Heliocentric Julian Day for blue band
14- 18 F5.3 --- Phasebc ? Phase for blue band (G1)
20- 24 F5.3 mag Dbcmag ? Differential blue comet continuum magnitude
4450/4467Å
26- 37 F12.4 d HJDgc Heliocentric Julian Day for green band
39- 43 F5.3 --- Phasegc Phase for green band (G1)
45- 49 F5.3 mag Dgcmag Differential green comet continuum magnitude
5260/5256Å
51- 62 F12.4 d HJDrc ? Heliocentric Julian Day for red band
64- 68 F5.3 --- Phaserc ? Phase for red band (G1)
70- 74 F5.3 mag Drcmag ? Differential red comet continuum magnitude
7128/7158Å
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Global notes:
Note (G1): Phase based on ephemeris 2444401.5916+0.201044004E determined
with a simple linear ephemeris that fits timings between 1980 and
2012; this is meant to be indicative, but not necessarily reliable.
Acknowledgements:
Andrew Odell, Andy.Odell(at)nau.edu
References:
Odell, 1984PASP...96..657O 1984PASP...96..657O, Period changes and a possible second pulsation
mode in BW Vul.
Odell, 1994IBVS.4138....1O 1994IBVS.4138....1O, Timings of selected variable stars.
(End) Andrew Odell [Flagstaff, Arizona], Patricia Vannier [CDS] 27-Jun-2012