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Model-based Interpretation of Cepheid spectra

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About this observation
Observer
Kevin Gurney
Time of observation
27/08/2019 - 00:05
Object
V1334 Cyg
Observing location
Sheffield
Equipment
Celestron C11
Shelyak Lhires III
Mesu 200 mount
Atik 460Ex
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High resolution spectra were taken of the Cepheid variable V1334
Cygni, around the H alpha absorption line, over five nights between
26th August 2019 and 6th September 2019. The observations were made
with a Shelyak Lhires III spectrograph and Celestron C11 OTA. I asked
the question: is it possible to see the Doppler shifts due to the
Cepheid pulsation with this rig?

The image shows a close up the H alpha lines around their minima which
are highlighted with blue-filled circles.  The spectra are plotted
with reference to the phase of the pulsation period (3.3 days) of the
Cepheid.  Note that all five are blue-shifted (the H alpha reference
is shown as the green dashed line).  Further, since a large range of the phase
variable is represented in these observations, this is not consistent
with a simple interpretation of pulsation and Doppler shift.

However,a recent model of V1334 Cyg [1] sheds some light here. Thus,
V1334 is a binary system with an orbital period of around 5.4
years. Over the limited time of my observations this gave a blue shift
shown by the red dashed line. The residual shifts oscillate back and
forth with respect to this value, and are indeed compatible with an
interpretation in terms of pulsation.

[A more complete report is available via the Spectroscopy forum page
https://britastro.org/node/19894]

[1] A. Gallenne, et al.  The Astrophysical Journal, 867(2):121,
November 2018.

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