J/AJ/169/340 W Serpentis light curve from A. Fresa taken in 1956 (Gies+, 2025)
TESS light curve of the interacting binary W Serpentis.
Gies D.R., Shepard K.A., Kar A., Richardson N.D.
<Astron. J., 169, 340 (2025)>
=2025AJ....169..340G 2025AJ....169..340G
ADC_Keywords: Binaries, eclipsing; Stars, double and multiple; Photometry;
Optical
Keywords: Interacting binary stars ; Eclipsing binary stars
Abstract:
The unusal light curve of the massive eclipsing binary W Ser was
recently observed with high S/N and fast cadence by the NASA TESS
mission. The TESS light curve records two eclipses and relatively fast
variations outside of the eclipses. The eclipse timings verify the
period increase of the binary, and the period derivative implies a
mass transfer rate in excess of 1e-5M☉/yr. The light curve
shows a fading trend from just after an eclipse until the start of the
next eclipse. The brightest flux source in the system is the accretion
torus surrounding the mass gainer star, and we argue that these
orbital-phase related fadings are the result of the injection of
cooler gas from the mass donor entering the outskirts of the accretion
torus. There are cyclic variations in the out-of-eclipse sections of
the light curve that vary on a 2.8day timescale. This equals the
orbital period for gas in the outer regions of the accretion torus, so
the photometric variations are probably the result of transitory,
overdense regions that form at the rim of the accretion torus.
Description:
A comparison of this paper's TESS light curve with that obtained by A.
Fresa (1957AJ.....62..362F 1957AJ.....62..362F) in 1956 provides us with a glimpse into
changes that have occurred over timescales of decades. A. Fresa (1957)
made photoelectric observations on 109 nights over between June 13 and
October 25 1956, and because of the diurnal sampling, these
measurements are useful to study variations on timescales longer than
2 days. The photometry was obtained at the Capodimonte Observatory in
Naples, Italy, with an unfiltered IP21 photocell that was sensitive to
flux in the 3000-6000Å range. A. Fresa (1957) estimated that the
orbital period was P=14.1563d in 1956.
The NASA TESS mission obtained its first light curve of W Ser over
26days in Sector 80 (June 18 - July 15, 2024) at a cadence of 200s.
The TESS spectral throughput corresponds to a band covering the
6000-10000Å range. We obtained the MIT Quick-Look Pipeline version
of the light curve from the Mikulski Archive for Space Telescopes6
(DOI:10.17909/tdkw-f793).
The 1956 light curve shows similar eclipses and the general flux
decline between eclipses as seen in the TESS light curve, but the
residuals from the fit show a larger dispersion, and there is a local
flux maximum near orbital phase 0.5 that is absent in the TESS light
curve.
Objects:
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RA (2000) DE Designation(s) (Period in 1956)
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18 09 50.64 -15 33 00.2 W Serpentis = HIP 88994 (Per = 14.1563d)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig4.dat 13 802 Photoelectric measurements taken in 1956 by A. Fresa
(1957AJ.....62..362F 1957AJ.....62..362F); Data behind Figure 4
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See also:
I/357 : Gaia DR3 Part 3. Non-single stars (Gaia Collaboration, 2022)
J/A+A/487/1129 : Evolutionary models of binaries (Van Rensbergen+, 2008)
J/A+A/618/A112 : β Lyr light curves (Mourard+, 2018)
http://archive.stsci.edu/doi/resolve/resolve.html?doi=10.17909/tdkw-f793 : MAST
data
Byte-by-byte Description of file: fig4.dat
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Bytes Format Units Label Explanations
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1- 7 F7.3 d HJD [638.4/772.3] Observation date; Heliocentric
Julian Date - 2,435,000d
9- 13 F5.2 mag dmag [-0.88/0.47] Magnitude difference
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History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 20-Mar-2026