J/AJ/150/97 Radial velocities in M67. I. 1278 candidate members (Geller+, 2015)
Stellar radial velocities in the old open cluster M67 (NGC 2682).
I. Memberships, binaries, and kinematics.
Geller A.M., Latham D.W., Mathieu R.D.
<Astron. J., 150, 97 (2015)>
=2015AJ....150...97G 2015AJ....150...97G (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Binaries, spectroscopic ; Radial velocities ;
Cross identifications
Keywords: binaries: spectroscopic - blue stragglers - methods: observational -
open clusters and associations: individual: NGC 2682 -
stars: kinematics and dynamics - techniques: spectroscopic
Abstract:
We present results from 13776 radial-velocity (RV) measurements of
1278 candidate members of the old (4Gyr) open cluster M67 (NGC 2682).
The measurements are the results of a long-term survey that includes
data from seven telescopes with observations for some stars spanning
over 40years. For narrow-lined stars, RVs are measured with precisions
ranging from about 0.1 to 0.8km/s. The combined stellar sample reaches
from the brightest giants in the cluster down to about 4mag below the
main-sequence turnoff (V=16.5), covering a mass range of about
1.34M☉ to 0.76M☉. Spatially, the sample extends to a
radius of 30arcmin (7.4pc in projection at a distance of 850pc or 6-7
core radii). We find M67 to have a mean radial velocity of +33.64km/s
(with an internal precision of ±0.03km/s) well separated from the
mean velocity of the field. For stars with ≥3 measurements, we derive
RV membership probabilities and identify RV variables, finding 562
cluster members, 142 of which show significant RV variability. We use
these cluster members to construct a color-magnitude diagram and
identify a rich sample of stars that lie far from the standard single
star isochrone, including the well-known blue stragglers,
sub-subgiants and yellow giants. These exotic stars have a binary
frequency of (at least) 80%, more than three times that detected for
stars in the remainder of the sample. We confirm that the cluster is
mass segregated, finding the binaries to be more centrally
concentrated than the single stars in our sample at the 99.8%
confidence level (and at the 98.7% confidence level when only
considering main-sequence stars). The blue stragglers are centrally
concentrated as compared to the solar-type main-sequence single stars
in the cluster at the 99.7% confidence level. Accounting for
measurement precision, we derive an RV dispersion in M67 of
0.80±0.04km/s for our sample of single main-sequence stars,
subgiants and giants with V≤15.5. When corrected for undetected
binaries, this sample yields a true RV dispersion of
0.59-0.06+0.07km/s. The radial distribution of the velocity
dispersion is consistent with an isothermal distribution within our
stellar sample. Using the cluster RV dispersion, we estimate a virial
mass for the cluster of 2100-550+610M☉.
Description:
This is the first in a series of papers studying the dynamical state
of the old open cluster M67 through precise radial velocities. This is
also the paper LXVII of the WIYN Open Cluster Study.
Our radial velocity survey of M67 began as part of the dissertation
work of Mathieu (1983PhDT.........8M 1983PhDT.........8M), taking advantage of the CfA
Digital Speedometers (DS). Three nearly identical instruments were
used, initially on the MMT (from HJD2445337 to HJD2450830) and 1.5m
Tillinghast Reflector (from HJD2444184 to HJD2454958) at the Fred
Lawrence Whipple Observatory on Mount Hopins, Arizona, and then later
on the 1.5m Wyeth Reflector (from HJD2445722 to HJD2453433) at the Oak
Ridge Observatory in the Town of Harvard, Massachusetts. Subsequently
the M67 target samples were expanded several times. Radial velocities
measurements from other programs were integrated into the database,
and our observational facilities were extended to include Hydra
Multi-Object Spectrograph (MOS) at the WIYN Observatory (from
HJD2453386 to HJD2456709) and the new Tillinghast Reflector Echelle
Spectrograph (TRES) on the Tillinghast Reflector (from HJD2455143 to
HJD2456801). Details about the telescopes, observing procedures, and
data reductions of spectra obtained with the CfA DS can be found in
Latham (1985srv..conf...21L, 1992ASPC...32..110L 1992ASPC...32..110L). The corresponding
information for spectra obtained with Hydra at the WIYN Observatory
can be found in Geller et al. 2008 (cat. J/AJ/135/2264), Geller et al.
2010 (cat. J/AJ/139/1383) and Hole et al. (2009). TRES is a stabilized
fiber-fed echelle spectrograph with a CCD detector and resolution of
44000.
The initial CfA sample was defined in 1982. The last surviving CfA
Digital Speedometer, on the 1.5m Tillinghast Reflector, was retired in
the summer of 2009. Over the following five observing seasons, TRES
was used to continue the radial velocity observations of targets
(mostly binaries) from both the CfA and the WIYN samples. Importantly,
Roger Griffin and James Gunn also had a radial velocity program for
M67 from 1971 to 1982 at the Palomar Hale 5m telescope (from
HJD2440952 to HJD2445297), which they supplemented with
contemporaneous observations obtained with the CORAVEL instrument
(from HJD2444340 to HJD2446413) at Haute Provence for five of the
binaries. Their target sample was very similar to our initial sample.
We refer to the target stars and the measurements taken at all
telescope/instrument pairs except WIYN/Hydra as the CfA sample and
data. As of 2015 February, there are 447 stars in the CfA sample.
WIYN observations of M67 began on 2005 January 15 as part of the WIYN
Open Cluster Study (WOCS; Mathieu, 2000ASPC..198..517M 2000ASPC..198..517M). In total
there are 1278 stars within the WIYN stellar sample; 382 of these
stars are also in the CfA stellar sample.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 162 1278 Radial-velocity data table
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See also:
B/gcvs : General Catalogue of Variable Stars (Samus+ 2007-2013)
J/A+A/545/A139 : Radial Velocities of stars observed in M67 (Pasquini+, 2012)
J/A+A/526/A127 : Velocities of M67 main-sequence and giant stars
(Pasquini+, 2011)
J/AJ/139/1383 : Radial velocities in M35 (NGC 2168) (Geller+, 2010)
J/AJ/138/159 : NGC 6819 stellar radial-velocity and photometry (Hole+, 2009)
J/AJ/135/2264 : Stellar radial velocities in NGC 188 (Geller+, 2008)
J/A+A/484/609 : BVI photometry and proper motions in M67 (Yadav+, 2008)
J/A+A/470/585 : NGC 2682 uvby-Hbeta photometry (Balaguer-Nunez+, 2007)
J/AJ/126/2954 : VI light curves of Sand 986 in M67 (Sandquist+, 2003)
J/A+A/382/899 : BVI photometry in M67 (Stassun+, 2002)
J/AJ/112/628 : BATC Color Survey of M67 (Fan+ 1996)
J/AJ/106/181 : CCD photometry of open cluster M67 (Montgomery+ 1993)
J/A+AS/100/243 : Proper motions in M 67 (Zhao+ 1993)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1 A1 --- f_WOCS [T] 'T' indicates a star taken from Mathieu et al.
(1986AJ.....92.1100M 1986AJ.....92.1100M, 1986AJ.....92.1364M 1986AJ.....92.1364M) (1)
2- 6 I5 --- WOCS [738/37055] WIYN Open Cluster Study (WOCS)
identifier (2)
8- 9 A2 --- r_OName [BFMSN ] Reference for OName (S, M, or F) (3)
10- 14 A5 --- OName ? Cross-reference identifier (4)
16 I1 h RAh Hour of Right Ascension (J2000)
18- 19 I2 min RAm Minute of Right Ascension (J2000)
21- 25 F5.2 s RAs Second of Right Ascension (J2000)
26 A1 --- DE- Sign of Declination (J2000)
27- 28 I2 deg DEd Degree of Declination (J2000)
30- 31 I2 arcmin DEm Arcminute of Declination (J2000)
33- 36 F4.1 arcsec DEs Arcsecond of Declination (J2000)
38 A1 --- Eq [JB] Equinox (J for Eq=J2000, B for Eq=B1950)
40- 45 F6.3 mag Vmag [7/21] The V-band magnitude (5)
47- 52 F6.3 mag B-V [-0.1/2.3]? The (B-V) color index (5)
54- 55 I2 --- NW [0/49] Number of WIYN sample radial velocity
measurements (6)
57- 59 I3 --- NC [0/991] Number of CfA sample radial velocity
measurements (6)
61- 68 F8.2 d MJD0 Modified Julian Date of first observation
(JD-2400000)
70- 77 F8.2 d MJD1 Modified Julian Date of last observation
(JD-2400000)
79- 85 F7.2 km/s [-151/187] Weighted mean radial velocity (7)
87- 91 F5.2 km/s e_ [0/45] Weighted standard error of (7)
93- 96 F4.2 km/s i [0.3/1.2]? Combined radial velocity precision (8)
98- 99 I2 % PRV [0/98]? Radial velocity membership probability (9)
101-103 I3 % PPMy [0/100]? Yadav et al. 2008 (cat. J/A+A/484/609)
proper-motion membership probability
105-106 I2 % PPMz [0/96]? Zhao et al. 1993 (cat. J/A+AS/100/243)
proper-motion membership probability
108-109 I2 % PPMg [0/99]? Girard et al. (1989AJ.....98..227G 1989AJ.....98..227G)
proper-motion membership probability
111-112 I2 % PPMs [0/96]? Sanders (1977A&AS...27...89S 1977A&AS...27...89S)
proper-motion membership probability
114-118 F5.2 --- e/i [0/57]? The e/i statistic (10)
120-124 F5.3 --- Pchi2 [0/1]? The P(χ2) value (11)
126-130 A5 --- Mm Membership classification (BLM, BLN, BM, BN,
BU, SM, SN, U) (12)
132-162 A31 --- Com Additional comment field (13)
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Note (1): Who use photometry from Murray & Clements (1968RGOB..139..309M 1968RGOB..139..309M).
Note (2): We follow the same method as Hole et al. 2009 (cat. J/AJ/138/159) to
define WOCS identifier based on the given star's V magnitude and distance
from the cluster center.
Note (3): The reference codes are defined as below:
S = If available the cross-reference identifier is taken from Sanders
1977A&AS...27...89S 1977A&AS...27...89S and denoted by the prefix "S";
M = If there is no Sanders (1977A&AS...27...89S 1977A&AS...27...89S) source match, we provide
the Montgomery et al. 1993 (cat. J/AJ/106/181) identifier, if
available;
F = If both of those studies lack a source match, we provide the Fan et al.
1996 (cat. J/AJ/112/628) identifiers, if available;
BN = This flag is not explained in the paper.
Note (4): There are 13 sources in our table that do not have matches in these
three references. As with all sources, we provide their RA and Dec
positions for matching to other catalogs.
Note (5): From Montgomery et al. 1993 (cat. J/AJ/106/181), where available. For
the few stars in our sample that are not in the Montgomery et al. 1993
(cat. J/AJ/106/181) survey and for which we can find no other BV photometry
from the literature, we derive V magnitudes from the 2MASS JHK photometry
using a similar relationship to Girard et al. (2004AJ....127.3060G 2004AJ....127.3060G). For
these stars, we do not have (B-V) colors.
Note (6): Counting radial velocities for primary stars only.
Note (7): For binaries with orbital solutions, we instead provide the
center-of-mass radial velocity.
Note (8): Defined as in Hole et al. 2009 (cat. J/AJ/138/159).
Note (9): We use the equation from Vasilevskis et al. 1958AJ.....63..387V 1958AJ.....63..387V:
PRV = Fc/Ff+Fc (Eq.(1) in the paper). We only compute membership
probabilities for stars with ≥3 observations. For non-RV-variable stars,
we use the weighted mean radial velocity (RV) in the calculations. For
binaries with orbital solutions, we use the γ-RV. For RV-variable
stars without orbital solutions, we cannot calculate a reliable radial
velocity (RV) membership probability, as the γ-RV is unknown. For
these stars we instead provide a preliminary membership classification.
Note (10): The ratio of the standard deviation (e) to the expected precision (i)
of the radial velocities for a given star.
Note (11): This statistic tests the hypothesis that a given star's distribution
of radial velocities is consistent with a constant value at the mean radial
velocity. See Section 5.1 for more details.
Note (12): The classes are defined in Section 5.3 and in Table 4 as follows:
SM = Single Member;
SN = Single Non-member;
BM = Binary Member;
BN = Binary Non-member;
BLM = Binary Likely Member;
BU = Binary with Unknown radial velocity membership;
BLN = Binary Likely Non-member;
U = Unknown radial velocity membership.
Note (13): We mark particularly notable stars within our stellar sample in this
comment field. We briefly discuss a few of these notable stellar
populations in Section 6.2 of the paper.
X = X-ray sources identified by Belloni et al. (1998A&A...339..431B 1998A&A...339..431B) with
ROSAT are labeled with "X" followed by the source number given in
their paper;
CX = Likewise X-ray sources identified by VandenBerg & Stetson
(2004PASP..116..997V 2004PASP..116..997V) with Chandra are labeled with "CX" followed by
the source number given in their paper;
PV = Photometric variables (Gilliland et al., 1991AJ....101..541G 1991AJ....101..541G),
Stassun et al. 2002 (cat. J/A+A/382/899), van den Berg et al.
(2002A&A...382..888V 2002A&A...382..888V), Sandquist & Shetrone 2003 (cat. J/AJ/126/2954,
2003AJ....125.2173S 2003AJ....125.2173S), Sandquist et al. (2003AJ....125..810S 2003AJ....125..810S), Qian et
al. (2006AJ....131.3028Q 2006AJ....131.3028Q), Bruntt et al. (2007MNRAS.378.1371B 2007MNRAS.378.1371B), Stello
et al. (2007MNRAS.377..584S 2007MNRAS.377..584S), Pribulla et al. (2008MNRAS.391..343P 2008MNRAS.391..343P),
Yakut et al., 2009A&A...503..165Y 2009A&A...503..165Y) are labeled with "PV," or "PV?" if
the authors identify the photometric variability as uncertain (e.g.,
possible flare event detections, possible nearby source contamination,
etc.);
RR = Stars that are rotating significantly more rapidly than our
instrumental resolution of ∼10km/s are labeled as "RR";
triple = Sources that are detected as triple systems;
BBS = Blue stragglers;
YG = Yellow giants;
SSG = Sub-subgiants.
We also label the W UMa's found in M67, and provide the GCVS names (see
cat. B/gcvs) for photometric variables, where available (e.g., AH Cnc,
ES Cnc, etc.).
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(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 22-Oct-2015