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تسجيل مستخدم جديدThe Second Data Release of the Survey of the MAgellanic Stellar History (SMASH)
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The Large and Small Magellanic Clouds (LMC and SMC) are the largest satellite galaxies of the Milky Way and close enough to allow for a detailed exploration of their structure and formation history. The Survey of the MAgellanic Stellar History (SMASH) is a community Dark Energy Camera (DECam) survey of the Magellanic Clouds using $sim$50 nights to sample over $sim$2400 deg$^2$ centered on the Clouds at $sim$20% filling factor (but with contiguous coverage in the central regions) and to depths of $sim$24th mag in $ugriz$. The primary goals of SMASH are to map out the extended stellar peripheries of the Clouds and uncover their complicated interaction and accretion history as well as to derive spatially-resolved star formation histories of the central regions and create a movie of their past star formation. Here we announce the second SMASH public data release (DR2), which contains all 197 fully-calibrated DECam fields including the main body fields in the central regions. The DR2 data are available through the Astro Data Lab hosted by the NSFs National Optical-Infrared Astronomy Research Laboratory. We highlight three science cases that make use of the SMASH DR2 data and will be published in the future: (1) preliminary star formation histories of the LMC; (2) the search for Magellanic star clusters using citizen scientists; and, (3) photometric metallicities of Magellanic Cloud stars using the DECam $u$-band.
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The Large and Small Magellanic Clouds (LMC and SMC) are unique local laboratories for studying the formation and evolution of small galaxies in exquisite detail. The Survey of the MAgellanic Stellar History (SMASH) is an NOAO community DECam survey o
f the Clouds mapping 480 square degrees (distributed over ~2400 square degrees at ~20% filling factor) to ~24th mag in ugriz with the goal of identifying broadly distributed, low surface brightness stellar populations associated with the stellar halos and tidal debris of the Clouds. SMASH will also derive spatially-resolved star formation histories covering all ages out to large radii from the MCs that will further complement our understanding of their formation. Here, we present a summary of the survey, its data reduction, and a description of the first public Data Release (DR1). The SMASH DECam data have been reduced with a combination of the NOAO Community Pipeline, PHOTRED, an automated PSF photometry pipeline based mainly on the DAOPHOT suite, and custom calibration software. The attained astrometric precision is ~15 mas and the accuracy is ~2 mas with respect to the Gaia DR1 astrometric reference frame. The photometric precision is ~0.5-0.7% in griz and ~1% in u with a calibration accuracy of ~1.3% in all bands. The median 5 sigma point source depths in ugriz bands are 23.9, 24.8, 24.5, 24.2, 23.5 mag. The SMASH data already have been used to discover the Hydra II Milky Way satellite, the SMASH 1 old globular cluster likely associated with the LMC, and very extended stellar populations around the LMC out to R~18.4 kpc. SMASH DR1 contains measurements of ~100 million objects distributed in 61 fields. A prototype version of the NOAO Data Lab provides data access, including a data discovery tool, SMASH database access, an image cutout service, and a Jupyter notebook server with example notebooks for exploratory analysis.
We present and make publicly available the second data release (DR2) of the Keck Observatory Database of Ionized Absorption toward Quasars (KODIAQ) survey. KODIAQ DR2 consists of a fully-reduced sample of 300 quasars at 0.07 < z_em < 5.29 observed wi
th HIRES at high resolution (36,000 <= R <= 103,000). DR2 contains 831 spectra available in continuum normalized form, representing a sum total exposure time of ~4.9 megaseconds on source. These co-added spectra arise from a total of 1577 individual exposures of quasars taken from the Keck Observatory Archive (KOA) in raw form and uniformly processed. DR2 extends DR1 by adding 130 new quasars to the sample, including additional observations of QSOs in DR1. All new data in DR2 were obtained with the single-chip Tektronix TK2048 CCD configuration of HIRES in operation between 1995 and 2004. DR2 is publicly available to the community, housed as a higher level science product at the KOA and in the igmspec database (v03).
The Galactic Archaeology with HERMES (GALAH) survey is a large-scale stellar spectroscopic survey of the Milky Way and designed to deliver chemical information complementary to a large number of stars covered by the $Gaia$ mission. We present the GAL
AH second public data release (GALAH DR2) containing 342,682 stars. For these stars, the GALAH collaboration provides stellar parameters and abundances for up to 23 elements to the community. Here we present the target selection, observation, data reduction and detailed explanation of how the spectra were analysed to estimate stellar parameters and element abundances. For the stellar analysis, we have used a multi-step approach. We use the physics-driven spectrum synthesis of Spectroscopy Made Easy (SME) to derive stellar labels ($T_mathrm{eff}$, $log g$, $mathrm{[Fe/H]}$, $mathrm{[X/Fe]}$, $v_mathrm{mic}$, $v sin i$, $A_{K_S}$) for a representative training set of stars. This information is then propagated to the whole survey with the data-driven method of $The~Cannon$. Special care has been exercised in the spectral synthesis to only consider spectral lines that have reliable atomic input data and are little affected by blending lines. Departures from local thermodynamic equilibrium (LTE) are considered for several key elements, including Li, O, Na, Mg, Al, Si, and Fe, using 1D MARCS stellar atmosphere models. Validation tests including repeat observations, Gaia benchmark stars, open and globular clusters, and K2 asteroseismic targets lend confidence in our methods and results. Combining the GALAH DR2 catalogue with the kinematic information from $Gaia$ will enable a wide range of Galactic Archaeology studies, with unprecedented detail, dimensionality, and scope.
The Large Magellanic Cloud (LMC) is the closest and most studied example of an irregular galaxy. Among its principal defining morphological features, its off-centred bar and single spiral arm stand out, defining a whole family of galaxies known as th
e Magellanic spirals (Sm). These structures are thought to be triggered by tidal interactions and possibly maintained via gas accretion. However, it is still unknown whether they are long-lived stable structures. In this work, by combining photometry that reaches down to the oldest main sequence turn-off in the colour-magnitude diagrams (CMD, up to a distance of $sim$4.4 kpc from the LMC centre) from the SMASH survey and CMD fitting techniques, we find compelling evidence supporting the long-term stability of the LMC spiral arm, dating the origin of this structure to more than 2~Gyr ago. The evidence suggests that the close encounter between the LMC and the Small Magellanic Cloud (SMC) that produced the gaseous Magellanic Stream and its Leading Arm (LA) also triggered the formation of the LMCs spiral arm. Given the mass difference between the Clouds and the notable consequences of this interaction, we can speculate that this should have been one of their closest encounters. These results set important constraints on the timing of LMC-SMC collisions, as well as on the physics behind star formation induced by tidal encounters.
We present the detection of very extended stellar populations around the Large Magellanic Cloud (LMC) out to R~21 degrees, or ~18.5 kpc at the LMC distance of 50 kpc, as detected in the Survey of the MAgellanic Stellar History (SMASH) performed with
the Dark Energy Camera on the NOAO Blanco 4m Telescope. The deep (g~24) SMASH color magnitude diagrams (CMDs) clearly reveal old (~9 Gyr), metal-poor ([Fe/H]=-0.8 dex) main-sequence stars at a distance of 50 kpc. The surface brightness of these detections is extremely low with our most distant detection having 34 mag per arcsec squared in g-band. The SMASH radial density profile breaks from the inner LMC exponential decline at ~13-15 degrees and a second component at larger radii has a shallower slope with power-law index of -2.2 that contributes ~0.4% of the LMCs total stellar mass. In addition, the SMASH densities exhibit large scatter around our best-fit model of ~70% indicating that the envelope of stellar material in the LMC periphery is highly disturbed. We also use data from the NOAO Source catalog to map the LMC main-sequence populations at intermediate radii and detect a steep dropoff in density on the eastern side of the LMC (at R~8 deg) as well as an extended structure to the far northeast. These combined results confirm the existence of a very extended, low-density envelope of stellar material with disturbed shape around the LMC. The exact origin of this structure remains unclear but the leading options include a classical accreted halo or tidally stripped outer disk material.
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