J/A+A/687/A273 Current and secular accretion rates of EX Hya (Beuermann+, 2024)
Current and secular accretion rates of EX Hydrae.
Beuermann K., Reinsch K.
<Astron. Astrophys. 687, A273 (2024)>
=2024A&A...687A.273B 2024A&A...687A.273B (SIMBAD/NED BibCode)
ADC_Keywords: Binaries, cataclysmic ; Binaries, X-ray ; Ephemerides ; Optical
Keywords: stars: evolution - novae, cataclysmic variables -
stars: individual: EX Hya - white dwarfs - Xrays: binaries
Abstract:
We report an observed accretion rate of
dM/dt1=(3.86±0.60)x10-11M☉/yr for the white dwarf in the
short-period, intermediate polar EX Hya. This result is based upon the
accretion-induced 4π-averaged energy flux from 2.45um to 100keV and
the corresponding luminosity at the Gaia distance of 56.77pc. Our
result is in perfect agreement with the theoretical mass transfer rate
from the secondary star induced by gravitational radiation (GR) and
the spin-up of the white dwarf,
-dM/dt2=(3.90±0.35)x10-11M☉/yr; 24% of it is caused by
the spin-up. The agreement indicates that mass transfer is
conservative. The measured dM/dt1 obviates the need for angular
momentum loss (AML) by any process other than GR. We complemented this
result with an estimate of the mean secular mass transfer rate over
∼107yr by interpreting the non-equilibrium radius of the secondary
star in EX Hya based on published evolutionary calculations. This
suggests a time-averaged mass transfer rate enhanced over GR by a
factor fGR≳2. Combined with the present-day lack of such an excess,
we suggest that an enhanced secular AML is due to an intermittently
active process, such as the proposed frictional motion of the binary
in the remnants of nova outbursts. We argue that EX Hya, despite its
weakly magnetic nature, has evolved in a very similar way to
non-magnetic CVs. We speculate that the discontinuous nature of an
enhanced secular AML may similarly apply to the latter.
Description:
Table 1 contains the spin maximum times of EX Hydrae measured from
AAVSO light curves taken between 2003 and 2023 by observers world wide
mostly in the Johnson V filter. The maximum times are estimated by eye
from online plots using the AAVSO tool LCGv2. The uncertainty is
estimated at 4 to 5 min.
Objects:
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RA (2000) DE Designation(s)
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12 52 24.22 -29 14 55.9 EX Hydrae = TIC 9560142
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 28 403 Measured times of spin phase maximum
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See also:
J/MNRAS/461/1576 : EX Hya mid-eclipse timings (Echevarria+, 2016)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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2- 4 I3 --- No Running number
7- 12 I6 --- E Cycle number (1)
15- 25 F11.5 d BJD Spin maximum time (TDB) (BJD-2400000) (2)
28 I1 --- Flag [1/2] Flag (3)
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Note (1): quadratic ephemeris of Mauche et al. (2009IBVS.5876....1M 2009IBVS.5876....1M)
Note (2): converted from UTC by the online tool
https://astroutils.astronomy.osu.edu/time/index.html
Note (3): Flag as follows:
1 = AAVSOdata
2 = for the two eclipses provided by C∼L. Duston of the
Merrimack College, MA 01845, USA.
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Acknowledgements:
Klaus Reinsch, klaus.reinsch(at)uni-goettingen.de
References:
Mauche et al., 2009IBVS.5876....1M 2009IBVS.5876....1M
Updated spin ephemeris for the cataclysmic variable EX Hydrae
(End) Patricia Vannier [CDS] 17-Jun-2024