skip to main content


Title: A uvbyCaHβ CCD Analysis of the Open Cluster Standard, M67, and Its Relation to NGC 752
Abstract

Precision CCDuvbyCaHβphotometry is presented of the old cluster, M67, covering one square degree with typical internal precision at the 0.005–0.020 mag level toV∼ 17. The photometry is calibrated using standards over a wide range in luminosity and temperature from NGC 752 and zeroed to the standard system via published photoelectric observations. Relative to NGC 752, differential offsets in reddening and metallicity are derived using astrometric members, supplemented by radial velocity information. From single-star members, offsets in the sense (M67−NGC 752) areδE(by) = −0.005 ± 0.001 (sem) mag from 327 F/G dwarfs andδ[Fe/H] = 0.062 ± 0.006 (sem) dex from the combinedm1andhkindices of 249 F dwarfs, leading toE(by) = 0.021 ± 0.004 (sem) and [Fe/H]M67= +0.030 ± 0.016 (sem) assuming [Fe/H]Hyades= +0.12. With probable binaries eliminated usingc1, (by) indices, 83 members with (π/σπ) > 50 generate (mM)0= 8.220 ± 0.005 (sem) for NGC 752 and an isochronal age of 1.45 ± 0.05 Gyr. Using the same parallax restriction for 312 stars, M67 has (mM) = 9.77 ± 0.02 (sem), leading to an age tied solely to the luminosity of the subgiant branch of 3.70 ± 0.03 Gyr. The turnoff color spread implies ±0.1 Gyr, but the turnoff morphology defines a younger age/higher mass for the stars, consistent with recent binary analysis and broadband photometry indicating possible missing physics in the isochrones. Anomalous stars positioned blueward of the turnoff are discussed.

 
more » « less
Award ID(s):
1909456
PAR ID:
10396945
Author(s) / Creator(s):
; ;
Publisher / Repository:
DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astronomical Journal
Volume:
165
Issue:
3
ISSN:
0004-6256
Format(s):
Medium: X Size: Article No. 105
Size(s):
Article No. 105
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    We have analyzed high-dispersion spectra in the Li 6708 Å region for 167 stars within the anticenter cluster NGC 2204. From 105 probable members, abundance analysis of 45 evolved stars produces [Fe/H] = −0.40 ± 0.12, [Si/Fe] = 0.14 ± 0.12, [Ca/Fe] = 0.29 ± 0.07, and [Ni/Fe] = −0.12 ± 0.10, where quoted errors are standard deviations. WithE(BV) = 0.07 and (mM)0= 13.12, appropriate isochrones provide an excellent match from the main sequence through the tip of the giant branch for an age of 1.85 ± 0.05 Gyr. Li spectrum synthesis producesA(Li) below 1.4 at the base of the red giant branch to a detectable value of −0.4 at the tip. Six probable asymptotic giant branch stars and all but one red clump star have only Li upper limits. A rapidly rotating red giant is identified as a possible Li-rich giant, assuming it is a red clump star. Main-sequence turnoff stars have a well-definedA(Li) = 2.83 ± 0.03 (sem) down to the Li-dip wall at the predicted mass of 1.29M. Despite having the same isochronal age as the more metal-rich NGC 2506, the luminosity distribution of red giants reflects a younger morphology similar to NGC 7789, possibly indicating a deeper impact of metallicity on stellar structure andA(Li) than previously assumed. As in NGC 2506 and NGC 7789, the NGC 2204 turnoff exhibits a broad range of rotation speeds, making abundance estimation impossible for some stars. The place of the cluster within GalacticA(Li) evolution is discussed.

     
    more » « less
  2. Abstract

    We present analyses of improved photometric and spectroscopic observations for two detached eclipsing binaries at the turnoff of the open cluster NGC 752: the 1.01 days binary DS And and the 15.53 days BD +37 410. For DS And, we findM1= 1.692 ± 0.004 ± 0.010M,R1= 2.185 ± 0.004 ± 0.008R,M2= 1.184 ± 0.001 ± 0.003M, andR2= 1.200 ± 0.003 ± 0.005R. We either confirm or newly identify unusual characteristics of both stars in the binary: the primary star is found to be slightly hotter than the main-sequence turnoff and there is a more substantial discrepancy in its luminosity compared to models (model luminosities are too large by about 40%), while the secondary star is oversized and cooler compared to other main-sequence stars in the same cluster. The evidence points to nonstandard evolution for both stars, but most plausible paths cannot explain the low luminosity of the primary star. BD +37 410 only has one eclipse per cycle, but extensive spectroscopic observations and the Transiting Exoplanet Survey Satellite light curve constrain the stellar masses well:M1= 1.717 ± 0.011MandM2= 1.175 ± 0.005M. The radius of the main-sequence primary star near 2.9Rdefinitively requires large convective core overshooting (>0.2 pressure scale heights) in models for its mass, and multiple lines of evidence point toward an age of 1.61 ± 0.03 ± 0.05 Gyr (statistical and systematic uncertainties). Because NGC 752 is currently undergoing the transition from nondegenerate to degenerate He ignition of its red clump stars, BD +37 410 A directly constrains the star mass where this transition occurs.

     
    more » « less
  3. Abstract

    We investigate barium (Ba) abundances in blue straggler stars (BSSs) in two open clusters, NGC 7789 (1.6 Gyr) and M67 (4 Gyr), as signatures of asymptotic-giant-branch (AGB) mass transfer. We combine our findings with previous Ba abundance analyses of NGC 6819 (2.5 Gyr) and NGC 188 (7 Gyr). Out of 35 BSSs studied in NGC 7789, NGC 6819, and M67, 15 (43% ± 11%) are Ba enriched; no BSSs in NGC 188 are Ba enriched. The Ba abundances of enriched BSSs show an anticorrelation with cluster age, ranging from an enrichment of [Ba/Fe] ∼ +1.5 dex in NGC 7789 to [Ba/Fe] ∼ +1.0 dex in M67. The Ba-enriched BSSs all lie in the same region of the H-R diagram, irrespective of cluster age or distance from the main-sequence turnoff. Our data suggest a link between AGB donor mass and mass-transfer efficiency in BSSs, in that less massive AGB donors tend to undergo more conservative mass transfer. We find that 40% ± 16% of the Ba-enriched BSSs are in longer-period spectroscopic binaries with orbital periods less than 5000 days. Those Ba-enriched BSSs that do not exhibit radial-velocity variability suggest AGB mass transfer in wide binaries by either wind mass transfer or wind Roche-lobe overflow. Given the preponderance of long orbital periods in the BSSs of M67 and NGC 188 and the frequency of Ba enrichment in NGC 7789, NGC 6819, and M67, it may be that AGB mass transfer is the dominant mechanism of BSS formation in open clusters older than 1 Gyr.

     
    more » « less
  4. Abstract

    We present stellar rotation periods for late K- and early M-dwarf members of the 4 Gyr old open cluster M67 as calibrators for gyrochronology and tests of stellar spin-down models. Using Gaia EDR3 astrometry for cluster membership and Pan-STARRS (PS1) photometry for binary identification, we build this set of rotation periods from a campaign of monitoring M67 with the Canada–France–Hawaii Telescope’s MegaPrime wide-field imager. We identify 1807 members of M67, of which 294 are candidate single members with significant rotation period detections. Moreover, we fit a polynomial to the period versus color-derived effective temperature sequence observed in our data. We find that the rotation of very cool dwarfs can be explained by simple solid-body spin-down between 2.7 and 4 Gyr. We compare this rotational sequence to the predictions of gyrochronological models and find that the best match is Skumanich-like spin-down,Prott0.62, applied to the sequence of Ruprecht 147. This suggests that, for spectral types K7–M0 with near-solar metallicity, once a star resumes spinning down, a simple Skumanich-like relation is sufficient to describe their rotation evolution, at least through the age of M67. Additionally, for stars in the range M1–M3, our data show that spin-down must have resumed prior to the age of M67, in conflict with the predictions of the latest spin-down models.

     
    more » « less
  5. ABSTRACT

    We present a detailed near-infrared chemical abundance analysis of 10 red giant members of the Galactic open cluster NGC 752. High-resolution (R ≃ 45000) near-infrared spectral data were gathered with the Immersion Grating Infrared Spectrograph, providing simultaneous coverage of the complete H and K bands. We derived the abundances of H-burning (C, N, O), α (Mg, Si, S, Ca), light odd-Z (Na, Al, P, K), Fe-group (Sc, Ti, Cr, Fe, Co, Ni), and neutron-capture (Ce, Nd, Yb) elements. We report the abundances of S, P, K, Ce, and Yb in NGC 752 for the first time. Our analysis yields solar-metallicity and solar abundance ratios for almost all of the elements heavier than the CNO group in NGC 752. O and N abundances were measured from a number of OH and CN features in the H band, and C abundances were determined mainly from CO molecular lines in the K band. High-excitation $\rm{C\,\small {I}}$ lines present in both near-infrared and optical spectra were also included in the C abundance determinations. Carbon isotopic ratios were derived from the R-branch band heads of first overtone (2−0) and (3−1) 12CO and (2−0) 13CO lines near 23 440 Å and (3−1) 13CO lines at about 23 730 Å. The CNO abundances and 12C/13C ratios are all consistent with our giants having completed ‘first dredge-up’ envelope mixing of CN-cyle products. We independently assessed NGC 752 stellar membership from Gaia astrometry, leading to a new colour–magnitude diagram for this cluster. Applications of Victoria isochrones and MESA models to these data yield an updated NGC 752 cluster age (1.52 Gyr) and evolutionary stage indications for the programme stars. The photometric evidence and spectroscopic light element abundances all suggest that the most, perhaps all of the programme stars are members of the helium-burning red clump in this cluster.

     
    more » « less