J/AJ/163/282 Radial velocity follow up of η Aquilae (Benedict+, 2022)
The η Aquilae System; Radial Velocities and Astrometry in Search of
η Aql B
Benedict G.F., Barnes T.G., Evans N.R., Cochran W.D., Anderson R.I.,
McArthur B.E., Harrison T.E.
<Astron. J., 163, 282 (2022)>
=2022AJ....163..282B 2022AJ....163..282B
ADC_Keywords: Stars, variable; Stars, double and multiple; Spectra, optical;
Spectra, infrared; Radial velocities
Keywords: Young disk Cepheid variable stars ; Cepheid variable stars
Abstract:
The classical Cepheid ηAql was not included in past Leavitt Law
work because of a presumed complicating orbit due to a known B9.8V
companion. To determine the orbit of ηAqlB, we analyze a
significant number of radial velocity (RV) measurements from eight
sources. With these we establish the RV variation due to Cepheid
pulsation, using a model with 12 Fourier coefficients, while solving
for velocity offsets required to bring the RV data sets into
coincidence. RV residuals provide no evidence of orbital motion,
suggesting either nearly face-on orientation or a very long period.
Reanalysis of Hubble Space Telescope Fine Guidance Sensor astrometry
now includes reference star parallax and proper motion priors from
Gaia EDR3. As modeling confirmation, we reanalyze ζGem in
parallel, deriving values for its parallax and proper motion
consistent with Gaia EDR3, and consistent with the Benedict 2007
Leavitt Law. In an effort to further characterize ηAqlB, we
hypothesize that ηAql residuals larger than those of the
associated reference stars or a parallax inconsistent with EDR3 and
the Benedict 2007 Leavitt Law indicate unmodeled orbital motion. Using
the astrometric noise or parallax mismatch with EDR3, we estimate
possible periods and mass for ηAqlB. Ascribing photocenter motion
to the photometric variation of the Cepheid, ηAqlA, yields a
plausible separation that is consistent with a long period and
explains the lack of RV variation. None of these approaches yields an
unassailable characterization of the ηAqlA-B system.
Description:
We revisit η Aql, now with new high-precision radial velocities
(RVs) from the Hobby-Eberly Telescope (HET), the Harlan J.Smith
telescope of McDonald Observatory (HJS), the Hermes Spectrograph on
the Mercator Telescope, and the Coralie spectrograph on the Euler
telescope.
We received HET High Resolution Spectrograph (HRS) time in four
scheduled trimesters, totaling 111 observations over 107 nights in the
interval 2010 August 10 - 2011 November 16. We used the 316g
cross-disperser, centered at 5936Å, with the echelle grating in the
"central" position. The spectrograph was fed with a fiber that
subtended 2" on the sky. We used a spectral resolving power of 60000
for all of the I2 cell observations.
Observations with the McDonald Observatory 2.7m Harlan J.Smith
Telescope were obtained using the Tull coude spectrograph. This
instrument is a cross-dispersed white-pupil echelle spectrograph
covering 3750-10200Å. A 1.2" entrance slit gave a spectral
resolving power of 60000.
We also had access to 217 radial velocities of η Aql from the 2m
Tennessee State University Automatic Spectroscopic Telescope (Eaton)
obtained over a period of two years: late 2007 to late 2009.
Objects:
-----------------------------------------------------------
RA (2000) DE Designation(s) (Period)
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19 52 28.37 +01 00 20.4 η Aql = * eta Aql (P=7.18d)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 45 95 HET radial velocities
table2.dat 45 51 HJS radial velocities
table3.dat 45 217 Eaton radial velocities
table4.dat 45 55 Coralie and Hermes radial velocities
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See also:
I/289 : UCAC2 Catalogue (Zacharias+ 2004)
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
J/ApJS/156/227 : Radial velocities of 16 Galactic Cepheids (Barnes+, 2005)
J/other/A+ARV/18.67 : Accurate masses and radii of normal stars (Torres+, 2010)
J/AJ/142/187 : HST observations of 7 Pop.II variable stars (Benedict+, 2011)
J/AJ/150/13 : Cepheid Radial Velocities (CRaV) project (Evans+, 2015)
J/A+A/584/A80 : Pulsation model data for delta Cep and eta Aql (Merand+, 2015)
J/ApJS/226/18 : 5yr radial velocity measurements 19 Cepheids (Anderson+, 2016)
J/ApJ/840/70 : Historical and HST Astrometry of Sirius A,B (Bond+, 2017)
J/A+A/631/A37 : Classic Cepheids consistent radial velocities (Borgniet+, 2019)
J/ApJS/254/42 : Hipparcos-Gaia (EDR3) Catalog of Accelerations (Brandt, 2021)
Byte-by-byte Description of file: table[1234].dat
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Bytes Format Units Label Explanations
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1 I1 --- Template ? Template spectrum ID for HET and HJS
3- 12 F10.4 d JD Date of observation; JD-2400000.0
14- 21 F8.6 --- Phase Cepheid pulsation phase
23- 29 F7.3 km/s RVel Radial Velocity (1)
31- 37 F7.5 km/s e_RVel Radial Velocity error
39- 45 A7 --- Inst Instrument used
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Note (1): See Table5 in the article for correction to absolute velocity.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 07-Oct-2022