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Register a new userThe Rotation of Selected Globular Clusters and the Differential Rotation of M3 in Multiple Populations from the SDSS-IV APOGEE-2 Survey
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In this paper, we analyze 10 globular clusters in order to measure their rotational properties by using high precision radial velocity data from the SDSS-IV APOGEE-2 survey. Out of the 10 clusters we were able to successfully measure the rotation speed and position angle of the rotation axis for 9 clusters (M2, M3, M5, M12, M13, M15, M53, M92, M107). The comparison between our results and previous ones shows a really good agreement within our uncertainties. For four of the globular clusters, M3, M13, M5 and M15, we separated the sample into two generation of stars using their [Al/Fe] abundances and examined the kinematic features of these generations separately from one another. In case of M3, we found significant difference between the rotational properties of first and second populations, confirming for the first time the predictions of several numerical simulations from the literature. The other three clusters (M5, M13, M15) also show smaller deviation between the two groups of stars, but those deviations are comparable to our errors.
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APOGEE-2 is a high-resolution, near-infrared spectroscopic survey observing roughly 300,000 stars across the entire sky. It is the successor to APOGEE and is part of the Sloan Digital Sky Survey IV (SDSS-IV). APOGEE-2 is expanding upon APOGEEs goals of addressing critical questions of stellar astrophysics, stellar populations, and Galactic chemodynamical evolution using (1) an enhanced set of target types and (2) a second spectrograph at Las Campanas Observatory in Chile. APOGEE-2 is targeting red giant branch (RGB) and red clump (RC) stars, RR Lyrae, low-mass dwarf stars, young stellar objects, and numerous other Milky Way and Local Group sources across the entire sky from both hemispheres. In this paper, we describe the APOGEE-2 observational design, target selection catalogs and algorithms, and the targeting-related documentation included in the SDSS data releases.
In the context of the ESO-VLT Multi-Instrument Kinematic Survey (MIKiS) of Galactic globular clusters, we present the line-of-sight rotation curve and velocity dispersion profile of M5 (NGC 5904), as determined from the radial velocity of more than 800 individual stars observed out to 700 (~ 5 half-mass radii) from the center. We find one of the cleanest and most coherent rotation patterns ever observed for globular clusters, with a very stable rotation axis (having constant position angle of 145^o at all surveyed radii) and a well-defined rotation curve. The density distribution turns out to be flattened in the direction perpendicular to the rotation axis, with a maximum ellipticity of 0.15. The rotation velocity peak (~3 km/s in projection) is observed at ~0.6 half-mass radii, and its ratio with respect to the central velocity dispersion (~0.3-0.4 at 4 projected half-mass radii) indicates that ordered motions play a significant dynamical role. This result strengthens the growing empirical evidence of the kinematic complexity of Galactic globular clusters and motivates the need of fundamental investigations of the role of angular momentum in collisional stellar dynamics.
APOGEE-2 is a dual-hemisphere, near-infrared (NIR), spectroscopic survey with the goal of producing a chemo-dynamical mapping of the Milky Way Galaxy. The targeting for APOGEE-2 is complex and has evolved with time. In this paper, we present the updates and additions to the initial targeting strategy for APOGEE-2N presented in Zasowski et al. (2017). These modifications come in two implementation modes: (i) Ancillary Science Programs competitively awarded to SDSS-IV PIs through proposal calls in 2015 and 2017 for the pursuit of new scientific avenues outside the main survey, and (ii) an effective 1.5-year expansion of the survey, known as the Bright Time Extension, made possible through accrued efficiency gains over the first years of the APOGEE-2N project. For the 23 distinct ancillary programs, we provide descriptions of the scientific aims, target selection, and how to identify these targets within the APOGEE-2 sample. The Bright Time Extension permitted changes to the main survey strategy, the inclusion of new programs in response to scientific discoveries or to exploit major new datasets not available at the outset of the survey design, and expansions of existing programs to enhance their scientific success and reach. After describing the motivations, implementation, and assessment of these programs, we also leave a summary of lessons learned from nearly a decade of APOGEE-1 and APOGEE-2 survey operations. A companion paper, Santana et al. (submitted), provides a complementary presentation of targeting modifications relevant to APOGEE-2 operations in the Southern Hemisphere.
Globular clusters (GCs) display anomalous light element abundances (HeCNONaMgAl), resembling the yields of hot-hydrogen burning, but there is no consensus yet on the origin of these ubiquitous multiple populations. We present a model in which a super-massive star (SMS, >10^3 Msun) forms via stellar collisions during GC formation and pollutes the intra-cluster medium. The growth of the SMS finds a balance with the wind mass loss rate, such that the SMS can produce a significant fraction of the total GC mass in processed material, thereby overcoming the so-called mass-budget problem that plagues other models. Because of continuous rejuvenation, the SMS acts as a `conveyer-belt of hot-hydrogen burning yields with (relatively) low He abundances, in agreement with empirical constraints. Additionally, the amount of processed material per unit of GC mass correlates with GC mass, addressing the specific mass budget problem. We discuss uncertainties and tests of this new self-enrichment scenario.
We present the first results of the Multi-Instrument Kinematic Survey of Galactic Globular Clusters, a project aimed at exploring the internal kinematics of a representative sample of Galactic globular clusters from the radial velocity of individual stars, covering the entire radial extension of each system. This is achieved by exploiting the formidable combination of multi-object and integral field unit spectroscopic facilities of the ESO Very Large Telescope. As a first step, here we discuss the results obtained for 11 clusters from high and medium resolution spectra acquired through a combination of FLAMES and KMOS observations. We provide the first kinematical characterization of NGC 1261 and NGC 6496. In all the surveyed systems, the velocity dispersion profile declines at increasing radii, in agreement with the expectation from the King model that best fits the density/luminosity profile. In the majority of the surveyed systems we find evidence of rotation within a few half-mass radii from the center. These results are in general overall agreement with the predictions of recent theoretical studies, suggesting that the detected signals could be the relic of significant internal rotation set at the epoch of the clusters formation.
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