J/A+A/511/L7 HR 7355 differential BV light curves (Mikulasek+, 2010)
HR 7355 - another rapidly braking He-strong CP star?
Mikulasek Z., Krticka J., Henry G.W., de Villiers S.N., Paunzen E., Zejda M.
<Astron. Astrophys. 511, L7 (2010)>
=2010A&A...511L...7M 2010A&A...511L...7M
ADC_Keywords: Stars, peculiar ; Photometry, UBV
Keywords: stars: chemically peculiar - stars: variables: general -
stars: individual: HR 7355 - stars: rotation
Abstract:
Strong meridional mixing induced by rapid rotation is one reason why
all hot main-sequence stars are not chemically peculiar. However,
the finding that the He-strong CP star HR 7355 is a rapid rotator
complicates this concept. Our goal is to explain the observed
behaviour of HR 7355 based on period analysis of all available
photometry. Over two years, we acquired 114 new BV observations of HR
7355 at observatories in Arizona, U.S.A and Cape Town, South Africa.
We performed period analyses of the new observations along with new
analyses of 732 archival measurements from the Hipparcos and ASAS
projects. We find that the light curves of HR 7355 in various filters
are quite similar, with amplitudes 0.035(4), 0.036(4), and 0.038(3)
mag in B, Hp, and V, respectively. The light curves are double-peaked,
with unevenly deep minima. We substantially refine the rotational
period to be P=0.5214410(4)d, indicating that HR 7355 is the most
rapidly rotating CP star known. Our period analyses reveal a possible
lengthening of the rotational period with (dP/dt)/P=2.4(8)x10-6yr-1.
We conclude that the shape and amplitude of HR 7355 light curves are
typical of magnetic He-strong CP stars, for which light variations are
the result of photospheric spots on the surface of a rotating star. We
hypothesise that the light variations are caused mainly by an uneven
distribution of overabundant helium on the star's surface. We briefly
describe and discuss the cause of the rapid rotational braking of the
star.
Description:
Differential BV photometry of the He strong CP star HR 5153=HD 182180
versus the comparison star HD 179520. Most of data was acquired by
G.W.Henry (GWH) with the T3 0.4-m automatic photoelectric telescope
(APT) at Fairborn Observatory in southern Arizona during 2008 May
and June. The T3 APT uses a temperature-stabilised EMI 9924B
photomultiplier tube to measure photon count rates sequentially
through B and V filters. We acquired there 43 B and 38 V measurements.
We also obtained 7 continuous hours of BV photometry with a
photoelectric photometer attached to a 0.28-m reflector on the night
of 2009 July 26 UT at the private observatory of S.N. de Villiers
(SNV) in Cape Town, South Africa. We acquired 16 and 17 measurements
in B and V.
Objects:
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RA (2000) DE Designation(s)
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19 24 30.2 -27 51 57 HR 7355 = HIP 95408
19 13 56.4 -26 52 35 HD 179520 = HIP 94491
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
bvphot.dat 35 81 BV difference of HR 7355 versus the comparison
HD 179520
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Byte-by-byte Description of file: bvphot.dat
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Bytes Format Units Label Explanations
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1- 12 F12.4 --- HJD Heliocentric Julian date
15- 21 F7.4 mag DBmag ? Variable minus comparison B magnitude
24- 30 F7.4 mag DVmag ? Variable minus comparison V magnitude
33- 35 A3 --- Obs Abbreviation of the observer (GWH, SNV)
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Acknowledgements:
Zdenek Mikulasek, mikulas(at)physics.muni.cz
(End) Zdenek Mikulasek [DTPA, Brno, Czech], Patricia Vannier [CDS] 23-Feb-2010