We here develop an improved way of using a rotating star as a clock, set it using the Sun, and demonstrate that it keeps time well. This technique, called gyrochronology, derives ages for low-mass main-sequence stars using only their rotation periods and colors. The technique is developed here and used to derive ages for illustrative groups of nearby field stars with measured rotation periods. We first demonstrate the reality of the interface sequence, the unifying feature of the rotational observations of cluster and field stars that makes the technique possible, and extend it beyond the proposal of Skumanich by specifying the mass dependence of rotation for these stars. We delineate which stars it cannot currently be used on. We then calibrate the age dependence using the Sun. The errors are propagated to understand their dependence on color and period. Representative age errors associated with the technique are estimated at ~15% (plus possible systematic errors) for late F, G, K, and early M stars. Gyro ages for the Mount Wilson stars are shown to be in good agreement with chromospheric ages for all but the bluest stars, and probably superior. Gyro ages are then calculated for each of the active main-sequence field stars studied by Strassmeier and collaborators. These are shown to have a median age of 365 Myr. The sample of single field stars assembled by Pizzolato and collaborators is then assessed and shown to have gyro ages ranging from under 100 Myr to several Gyr, with a median age of 1.2 Gyr. Finally, we demonstrate that the individual components of the three wide binaries ξ Boo AB, 61 Cyg AB, and α Cen AB yield substantially the same gyro ages.

https://iopscience.iop.org/article/10.1086/519295/pdf

Ages for illustrative field stars using gyrochronology: viability, limitations and errors

Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) is an optical fiber-bundle integral-field unit (IFU) spectroscopic survey that is one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV). With a spectral coverage of 3622 - 10,354 Angstroms and an average footprint of ~ 500 arcsec^2 per IFU the scientific data products derived from MaNGA will permit exploration of the internal structure of a statistically large sample of 10,000 low redshift galaxies in unprecedented detail. Comprising 174 individually pluggable science and calibration IFUs with a near-constant data stream, MaNGA is expected to obtain ~ 100 million raw-frame spectra and ~ 10 million reduced galaxy spectra over the six-year lifetime of the survey. In this contribution, we describe the MaNGA Data Reduction Pipeline (DRP) algorithms and centralized metadata framework that produces sky-subtracted, spectrophotometrically calibrated spectra and rectified 3-D data cubes that combine individual dithered observations. For the 1390 galaxy data cubes released in Summer 2016 as part of SDSS-IV Data Release 13 (DR13), we demonstrate that the MaNGA data have nearly Poisson-limited sky subtraction shortward of ~ 8500 Angstroms and reach a typical 10-sigma limiting continuum surface brightness mu = 23.5 AB/arcsec^2 in a five arcsec diameter aperture in the g band. The wavelength calibration of the MaNGA data is accurate to 5 km/s rms, with a median spatial resolution of 2.54 arcsec FWHM (1.8 kpc at the median redshift of 0.037) and a median spectral resolution of sigma = 72 km/s.

/pdf/the-data-reduction-pipeline-for-the-sdss-iv-manga-ifu-galaxy-35pda87eee.pdf

The Data Reduction Pipeline for the SDSS-IV MaNGA IFU Galaxy Survey

We present a chemical abundance analysis based on high resolution UVES spectra of seventeen bright giant stars in the Globular Cluster (GC) M 22. We obtained an average iron abundance of [Fe/H] = −1.76 ± 0.02 (internal errors only) and an α enhancement of 0.36 ± 0.04 (internal errors only). Na and O, and Al and O follow the well known anticorrelations found in many other GCs. We identified two groups of stars with significantly different abundances of the s-process elements Y, Zr, and Ba. The relative numbers of the two group members are very similar to the ratio of the number of stars in the two sub giant branches (SGB) of M 22. Y and Ba abundances do not correlate with Na, O, and Al. The s-element rich stars are also richer in iron and have higher Ca abundances. The results from high resolution spectra were confirmed by analyses of lower resolution GIRAFFE spectra of fourteen additional M 22 stars. The analyses of the GIRAFFE spectra also show that the Eu – a pure r-process element – abundance is not related to the iron content. We discuss the chemical abundance pattern of M 22 stars in the context of GC multiple stellar populations phenomenon.

/pdf/a-double-stellar-generation-in-the-globular-cluster-ngc-6656-49otqsg31g.pdf

A double stellar generation in the globular cluster NGC 6656 (M 22): Two stellar groups with different iron and s-process element abundances

Context. Two main scenarios for the formation of the Galactic bulge are invoked, the first one through gravitational collapse or hierarchical merging of subclumps, the second through secular evolution of the Galactic disc.Aims. We aim to constrain the formation of the Galactic bulge through studies of the correlation between kinematics and metallicities in Baade's Window (l = 1°, b = -4°) and two other fields along the bulge minor axis (l = 0°, b = -6° and b = -12°).Methods. We combine the radial velocity and the [Fe/H] measurements obtained with FLAMES/GIRAFFE at the VLT with a spectral resolution of R = 20 000, plus for the Baade's Window field the OGLE-II proper motions, and compare these with published N -body simulations of the Galactic bulge.Results. We confirm the presence of two distinct populations in Baade's Window found in Hill et al. (2010, A&A, submitted): the metal-rich population presents bar-like kinematics while the metal-poor population shows kinematics corresponding to an old spheroid or a thick disc. In this context the metallicity gradient along the bulge minor axis observed by Zoccali et al. (2008, A&A, 486, 177), visible also in the kinematics, can be related to a varying mix of these two populations as one moves away from the Galactic plane, alleviating the apparent contradiction between the kinematic evidence of a bar and the existence of a metallicity gradient.Conclusions. We show evidence that the two main scenarios for the bulge formation co-exist within the Milky Way bulge.

/pdf/insights-on-the-milky-way-bulge-formation-from-the-45ket4go60.pdf

Insights on the Milky Way bulge formation from the correlations between kinematics and metallicity

We combine spectroscopic and photometric data for subgiant stars of ω Cen to extract results that neither data set could have provided on its own. GIRAFFE@VLT spectra of 80 stars at R = 6400 give metallicities for all of them and abundances of C, N, Ca, Ti, and Ba for a subset of them. The photometric data, which have unusually high accuracy, come from a ~10 × 10 arcmin2 mosaic of HST ACS images centered on the cluster center and on multicolor images of a ~34 × 33 arcmin2 field, taken with the WFI@ESO2.2m camera. Stars with [Fe/H] < -1.25 have a large magnitude spread on the flat part of the SGB. We interpret this as empirical evidence for an age spread, and from theoretical isochrones we derive a relative age for each star. Within the SGB region we identify four distinct stellar groups: (1) an old, metal-poor group ([Fe/H] ~ -1.7); (2) an old, metal-rich group ([Fe/H] ~ -1.1); (3) a young (up to 4-5 Gyr younger than the old component) metal-poor group ([Fe/H] ~ -1.7); (4) a young, intermediate-metallicity ([Fe/H] ~ -1.4) group, on average 1-2 Gyr younger than the old metal-poor population, and with an age spread that we cannot properly quantify with the present sample. In addition, many SGB stars are spread between the intermediate-metallicity and metal-rich branches. We tentatively propose connections between the SGB stars and both the multiple main-sequence and the red giant branches. Finally, we discuss the implications of the multiple stellar populations on the formation and evolution of ω Cen. The spread in age within each population establishes that the original system must have had a composite nature.

http://iopscience.iop.org/article/10.1086/517905/pdf

The multiplicity of the subgiant branch of ω centauri : Evidence for prolonged star formation

A brief overview is given of the data-reduction software (DRS) being developed at Geneva and Paris Observatories for the fiber-fed multi-object GIRAFFE spectrograph - part of the VLT FLAMES facility. The specific aspects of each of three modes is presented and discussed. The localization and the extraction are described in more details, the original features are outlined and the critical issue addressed. We discuss the problem of the PSF variation across the surface of the detector and the impact on the sky subtraction. The strategy of the real-time data quality assessment using the simultaneous calibration exposure is described. Some aspect of the DRS implementation and the VLT environment are discussed. The dirty prototype of the DRS under Matlab including the crude instrument simulator is discussed and some experiments measuring the expected accuracy of radial- velocity are shown.

Data-reduction software for GIRAFFE, the VLT medium-resolution multi-object fiber-fed spectrograph

We describe briefly the Data-Reduction of the VLT fiber-fed multi-object GIRAFFE spectrograph - part of the VLT FLAMES facility. We focus on specific features of GIRAFFE - the simultaneous wavelength calibration - and their impact on the data-reduction strategy. We describe the implementation of the global physical model and we compare the results obtained with the simulated, laboratory and preliminary data. We discuss the influence of critical parameters, the overall accuracy of the wavelength solution, and the stability and the robustness of the global model approach . We address the accuracy of radial velocity measurements illustrated by solar spectra obtained during the Preliminary Acceptance in Europe.

Toward accurate radial velocities with the fiber-fed GIRAFFE multi-object VLT spectrograph.

In this paper we present the development of a CCD imager for the modern 1.2m MERCATOR telescope dedicated to long term monitoring of variable astrophysical phenomena. This instrument is a result of the collaboration of the Observatory of Geneva with the Institute of Astronomy in Leuven. After a technical description of the main components of the CCD camera system, the text will focus on the automatization of the observations and subsequent data reduction. The telescope itself is an altazimuth mounted 1.2 m Ritchey-Chretien telescope and is operated in a semi-automatic mode. The system executes a predefined sequence of observations, that only need
occasional checking of data quality by the astronomer. The observation software is written in a FORTRAN based interpreter language (INTER) running on a UNIX system that communicates with the astronomer via GUIs implemented in Perl/Tk. The data reduction is integrated into one package and includes pre-reduction, photometric and astrometric calibration, extraction, catalogue preparation and archiving. This allows to have a GUI driven reduction that is both flexible and robust. The preliminary reduced data give the astronomers an indication of the quality of their observations, so that they can adjust their program or camera settings during the same night.

CCD camera and automatic data reduction pipeline for the Mercator telescope on La Palma

Fully autmated high-resolution spectroscopy at Swiss 1.2 m La silla telescope

A Ritchey-Chretien 1.2 m telescope (EULER) and the High- Resolution echelle Spectrograph (CORALIE), a new Swiss observing facility at ESO La Silla Observatory, are operational and since Summer 1998. The Observatory operation is fully automated and supports the unattended, attended and interactive mode of operation under local or remote control. The control hardware is based on Local Control Units (LCU) built from PC/RedHat Linux computers and a Unix Computing Server. The Operational Software is built around INTER, a command language interpreter featuring communication control, data access, image processing functions and easy access to external resources. The general SW architecture is a non-hierarchical tree of pairs made of hardware- independent interpreters running on the Observing Server and hardware dependent servers running on the LCU's. The Operational Software includes the full access (Creation/Modification/Retrieval) to the input/output databases, telescope, instrument and auxiliary set-up and control files as well as a full data-reduction pipeline. We describe briefly the system architecture, summarize the performances and the experience gained over 18 months of operation and we discuss some critical issues: use of standard components, parallel operation, real-time requirements, system upgrade and maintenance.

Fully automated high-resolution spectroscopy at Swiss 1.2 m La Silla telescope

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