J/AJ/169/46 Plaskett's star photographic spectra from DAO (Davidge, 2025)
Old dogs, new tricks: Re-examining photographic spectra of Plaskett's star.
Davidge T.J.
<Astron. J., 169, 46 (2025)>
=2025AJ....169...46D 2025AJ....169...46D
ADC_Keywords: Spectra, optical; Stars, O; Stars, double and multiple;
Plate data; Photographic catalog; Binaries, spectroscopic
Keywords: O stars ; Spectroscopic binary stars
Abstract:
Photographic spectra of Plaskett's Star (HR 2420, HD 47129, V640
Monocerotis) that were recorded at the Dominion Astrophysical
Observatory have been digitized with a flatbed scanner. Many of the
spectra were recorded during campaigns in 1922 and 1937, and cover
wavelengths between 0.39 and 0.50um. Spectra of poor quality are
identified. Mean spectra near orbital phases 0.25 and 0.75 match many
characteristics of synthetic spectra, although Hγ and He i
λ4388 are exceptions. Evidence is presented that Hγ was
affected by transient activity in 1937, but not in 1922. Emission
lines of N iii and He ii move with wavelength in a manner that is
consistent with them tracking the motion of the secondary, indicating
that an "f" spectral type designation should be assigned to the
secondary. The location of the peak that is associated with the
secondary in cross-correlation functions changes with time near phase
0.75, although the mean amplitude of the radial velocity curve of the
secondary did not change between the two campaigns. There is also an
offset in velocities of the primary measured from Hγ and He i
λ4472 near phase 0.25. The velocity curves of the components
suggest a mass ratio that is larger than previous estimates, although
uncertainties associated with the spectroscopic features attributed to
the secondary, coupled with the wavelength resolution of the spectra,
complicate efforts to determine robust masses. We conclude that the
peculiarities in the radial velocity curves of the components have
thus been in place for over a thousand orbital cycles.
Description:
The Dominion Astrophysical Observatory (DAO) in British Columbia,
Canada, hosts a large collection of photographic spectra that were
recorded on its telescopes over much of the past century. The largest
number of plates were recorded with the original Cassegrain
spectrograph on the 1.8m telescope, starting in 1918, while the Coude
spectrograph on the 1.2m telescope has been in use since 1962.
In the current paper, we examine digitized photographic spectra of the
binary system Plaskett's Star (hereafter PS). PS was targeted early
in the operational life of the 1.8m telescope as part of a survey of
emission-line O stars, and it was soon found to be a double-line
spectroscopic binary (SB2).
The 1.8m spectra were recorded from 1921 to 1954 through a slit with a
prism as the dispersing element. The wavelength coverage extends from
0.39 to 0.50um. Most of the spectra were recorded with the
medium-focus 28Å/mm camera, although some were recorded with the
short-focus 55Å/mm camera. The 1.8m spectra from the 1920 and 1930s
were recorded on Eastman 40 plates that were probably not
hypersensitized.
The 1.2m spectra were recorded from 1969 to 1975 with an image slicer.
The majority of these spectra were recorded with the 32121 grating
mosaic (10.1Å/mm), although some spectra were also recorded with
the 3262 (9.0Å/mm) and 3282 (6.5Å/mm) gratings. The wavelength
coverage of the 1.2m spectra typically extends from 0.35 to 0.55um,
and we place emphasis on the 0.39-0.50um interval for compatability
with the 1.8m spectra. The 1.2m spectra were recorded on Kodak Type II
or III plates with wavelength responses tuned to sample near-UV to
visible wavelengths.
Objects:
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RA (2000) DE Designation(s)
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06 37 24.04 +06 08 07.3 Plaskett's star = HD 47129 = V* 640 Mon
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 86 83 Plaskett's star spectra and plates information from
1.8m DAO telescope observations
table2.dat 79 25 Plaskett's star spectra and plates information from
1.2m DAO telescope observations
fig1_fits/* . 78 Individual FITS file of the 1.8m DAO telescope
observations
fig2_fits/* . 24 Individual FITS file of the 1.2m DAO telescope
observations
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See also:
B/dao : DAO Science Archive observations (CADC, 2020)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Plate Plate number
9- 18 A10 "Y/M/D" Date Date of observation (YYYY-MM-DD)
20- 28 F9.3 --- HJD Heliocentric Julian Date of observation
(HJD - 2400000)
30- 34 F5.3 --- Phase Orbital Phase (1)
36- 60 A25 --- Notes Additional information (2)
62- 63 A2 --- Sp Associated spectrum at HJD with link to
interactive plot (column added by CDS)
65- 86 A22 --- FITS Link to the spectrum file in FITS format (column
added by CDS)
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Note (1): From orbital elements in Table 2 of Linder+ (2008A&A...489..713L 2008A&A...489..713L).
Note (2): Most spectra were recorded with the medium-focus 29Å/mm camera,
while a small number were recorded with the short-focus 55Å/mm
camera. The spectra with an "Alignment" entry in the last column have
blurred lines and an uneven response with wavelength. It is suspected
that these problems were due to unstable optical alignment in the
spectrograph.
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- Plate Plate number
6- 15 A10 "Y/M/D" Date Date of observation (YYYY-MM-DD)
17- 25 F9.3 --- HJD Heliocentric Julian Date of observation
(HJD - 2400000)
27- 31 F5.3 --- Phase Orbital phase (1)
33- 55 A23 --- Notes Additional information (2)
57- 58 A2 --- Sp Associated spectrum at HJD with link to
interactive plot (column added by CDS)
60- 79 A20 --- FITS Link to the spectrum file in FITS format (column
added by CDS)
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Note (1): From orbital elements in Table 2 of Linder+ (2008A&A...489..713L 2008A&A...489..713L).
Note (2): Most of the spectra were recorded with the 32121 grating mosaic
(10.1Å/mm). Plates identified as having poor cosmetics are
affected by nonuniformities in development and/or fingerprints.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 14-Nov-2025