J/AJ/80/379 Hyades cluster: motion, membership, and distance (Hanson+, 1975)
A study of the motion, membership, and distance of the Hyades cluster
Hanson R.B.
<Astron. J. 80, 379 (1975)>
=1975AJ.....80..379H 1975AJ.....80..379H
ADC_Keywords: Clusters, open ; Proper motions
Abstract:
New absolute proper motions referred directly to external galaxies,
photographic photometry, and cluster membership probabilities have
been determined for over 600 faint stars in the Hyades region. These
have been used to investigate the Hyades convergent point and
distance. A detailed review of the foundations of the convergent-point
method, its applicability to the Hyades, the several mathematical
variations of the method, and its possible role in producing the
apparent discrepancy between previous Hyades proper motion results and
"secondary" Hyades distance indicators, has been carried out. The
convergent-point method, as applied to the Hyades, is entirely valid,
and cannot be the source of any significant error in the Hyades
distance. Systematic errors in meridian circle proper motions are
implicated as the cause of the observed Hyades distance discrepancy.
The convergent-point analysis of the new absolute Hyades proper
motions represents the first Hyades distance determination independent
of all meridian circle proper motion systems. The resulting Hyades
distance modulus is m-M=3.42, significantly greater than all previous
values from proper motions, and in agreement with predictions of the
Hyades distance from stellar structure theory, and with the results of
"secondary" distance indicators. Incorporating this value, the most
likely value of the mean Hyades distance modulus from all sources is
m-M=3.29±0.08. The quoted error represents a larger and more
realistic estimate of the true errors than has been previously stated.
Significant effects of the increased Hyades distance on the cosmic
distance scale and other questions of general astronomical importance
are briefly discussed.
Description:
Particular attention is given to the role of the convergent-point, or
moving cluster, method in the determination of the Hyades distance,
and the apparent discrepancy between its results and those of other
Hyades distance indicators. The Hyades photographic plate material is
considered along with the approaches used in the measurements, proper
motion reductions, coordinate reductions, and aspects of photography.
Problems of cluster membership determination are also discussed.
The proper motion data were obtained from the Lick 20-in.(51cm) double
astrograph plates observed over a period of 24.1years (1948 to 1973):
1948-11-27, 1958-01-14, 1963-01-25, 1970-10-04, 1973-01-03.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 99 617 Identifications, positions, magnitudes, proper
motions, and Hyades membership probabilities
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
2- 4 I3 --- Star Star number
<Cl* Melotte 25 Han NNN> in Simbad
6- 8 I3 --- VA ? Van Altena number
(1966AJ.....71..482V 1966AJ.....71..482V, 1969AJ.....74....2V 1969AJ.....74....2V)
10- 17 A8 --- Luyten Luyten designation (1971hyad.book.....L 1971hyad.book.....L,
University of Minnesota)
19- 20 I2 h RAh Right ascension (B1950, Epoch=1948.91)
22- 23 I2 min RAm Right ascension (B1950, Epoch=1948.91)
25- 29 F5.2 s RAs Right ascension (B1950, Epoch=1948.91)
31 A1 --- DE- Declination sign
32- 33 I2 deg DEd Declination (B1950, Epoch=1948.91)
35- 36 I2 arcmin DEm Declination (B1950, Epoch=1948.91)
38- 42 F5.2 arcsec DEs Declination (B1950, Epoch=1948.91)
44- 48 F5.2 mag Vmag ? V magnitude, from yellow and blue plates
50- 54 F5.2 mag B-V ? B-V colour index
57 I1 --- T [2/5]? Star type (1)
60 I1 --- S [1/3]? System (exposure) code (2)
63- 67 I05 --- Nm Number of images measured at each epoch (4)
69- 74 F6.3 arcsec/yr pmRA Proper motion in right ascension
76- 81 F6.3 arcsec/yr pmDE Proper motion in declination
84- 86 I3 mas/yr e_pmRA Error on proper motion in RA
89- 91 I3 mas/yr e_pmDE Error on proper motion in DE
96- 97 I2 % Mmb [0/99] Hyades membership probability
99 I1 --- Note [1/4]? Note (3)
--------------------------------------------------------------------------------
Note (1): the code for the type of star takes the following values:
2 = faint reference star
3 = AGK 2 catalogue star
4 = photoelectric photometry star
5 = selected on blink survey
Note (2): the exposures used are indicated with the following code:
1 = long exposure
2 = short exposure
3 = both exposures
Note (3): Remarks are coded at follows:
1 = No yellow plate measures; approximate B magnitudes are:
Star#34=18.04; Star#332=13.40; Star#395=18.57;
Star#404=18.12; Star#406=18.72; Star#575=17.87.
2 = Image interference on blue plates with nearby bright star; (B-V) suspect.
3 = Near plate edge. (B-V) suspect.
4 = Severe image interference on plates.
* No. 350: Only first-epoch position measurable.
* No. 616: OS 996, near α Tau, all data may be suspect.
Bmag∼11.9.
Note (4): Each digit represents the number of images for the 5 epochs
1948.91, 1958.04, 1963.07, 1970.76, 1973.01
--------------------------------------------------------------------------------
Historical Notes:
* 30-Aug-1995: Keypunched at CDS
* 20-Nov-2013: Standardized, documentation completed.
(End) Marie-Jose Wagner, Simona Mei [CDS] 30-Aug-1995