Found 24 talks archived in Catalogs and data
I've heard many times about the Virtual Observatory, but what really is VO? Is it just for IT people?, for data centres?, for astronomers?, for everybody? Who is behind VO? Is the Virtual Observatory sustainable in the medium-term? Was it just a nice idea or is it really having an impact on the way astronomers make science with archive data?
In this talk I'll try to answer all these questions by describing the Spanish Virtual Observatory, an initiative that began in 2004 with the aim of coordinating at national level the VO-related activities in four different fields.
Special focus will be given to usage examples of VO tools for real VO-science projects.
The IAC is the only Spanish Institution participating as a full member in SDSS-III (2009-2014). The survey finishes in June 2014, and will publicly release all data by the end of the year, including H-band high-resolution spectra for 100,000 stars in the Milky Way and optical mid-resolution spectra for 1.5 million LRGs and 160,000 quasars.
SDSS-IV will immediately follow, including spectroscopic surveys of variable sources, x-ray source follow-up observations, galaxy and quasar redshifts, Integral-field-unit spectroscopy of galaxies and high-resolution infrared spectroscopy of galactic stars, organized in the following projects: Time-Domain Spectroscopic Survey (TDSS), SPectroscopic IDentification of ERosita Sources (SPIDERS), Extended Baryon Oscillation Spectroscopic Survey (eBOSS), Mapping Nearby Galaxies at APO (MaNGA), and the APO Galaxy Evolution Experiment 2 (APOGEE-2).
The participation of the IAC in SDSS is gaining strength. As an example, in the first half of 2013, about 13% of the papers published by IAC researchers used SDSS data, and these papers contributed 33% of the citations received by the IAC in the same period. We will provide an overview of SDSS activities at the IAC, and current plans for participating in SDSS-IV (2014-2020).
This has been an exciting year for the SDSS-III collaboration. BOSS has made spectacular progress and it is running 6 months ahead of schedule. APOGEE has secured ~ 300,000 spectra for 50,000 stars, mostly red giants and nearly half of its total sample. The APOGEE Stellar Parameter and Chemical Abundance Pipeline is providing reliable atmospheric parameters, including metallicities. Data Release 10 (DR10) will take place next summer, but DR10 BOSS data are already available to the collaboration, and DR10 APOGEE data products will be internally released in the next few weeks. SDSS activity is growing at the IAC. We will report on SDSS-III news and SDSS-IV prospects, including an overview of the SDSS-IV programs APOGEE-2, eBOSS (+TDSS+SPIDERS), and MaNGA.
The IAC started in June 2010 its participation as an institutional member in the current phase of the Sloan Digital Sky Survey (SDSS-III). In the last year there has been plenty of news in all four projects of the survey: BOSS, MARVELS, SEGUE-2 and APOGEE. In this talk we will summarize the main results, give a progress report, describe the next public data release (DR9), and highlight the contributions and involvement at the IAC. SDSS-III will end in 2014, and we will provide a glimpse of what is coming up afterward.
We compare the Hubble type and the spectroscopic class of the galaxies with spectra in SDSS/DR7. As it is long known, elliptical galaxies tend to be red whereas spiral galaxies tend to be blue, however, this relationship presents a large scatter, which we measure and quantify in detail. We compare the Automatic Spectroscopic K-means based classification (ASK) with most of the commonly used morphological classifications. All of them provide consistent results. Given a spectral class, the morphological type wavers with a standard deviation between 2 and 3 T types, and the same large dispersion characterizes the variability of spectral classes fixed the morphological type. The distributions of Hubble types given an ASK class are very skewed -- they present long tails that go to the late morphological types for the red galaxies, and to the early morphological types for the blue spectroscopic classes. The scatter is not produced by problems in the classification, and it remains when particular subsets are considered. A considerable fraction of the red galaxies are spirals (40--60 %), but they never present very late Hubble types (Sd or later). Even though red spectra are not associated with ellipticals, most ellipticals do have red spectra: 97 % of the ellipticals in the morphological catalog by Nair & Abraham, used here for reference, belong to ASK 0, 2 or 3. It contains only a 3 % of blue ellipticals. The galaxies in the green valley class (ASK~5) are mostly spirals, and the AGN class (ASK 6) presents a large scatter of Hubble types from E to Sd. We investigate variations with redshift using a volume limited subsample. From redshift 0.25 to now the galaxies redden from ASK 2 to ASK 0, as expected from the passive evolution of their stellar populations. Two of the ASK classes (1 and 4) gather edge-on spirals, and they may be useful in studies requiring knowing the intrinsic shape of a galaxy (e.g., weak lensing calibration).
Since June last year, the IAC is an institutional member in the third phase of the Sloan Digital Sky Survey (SDSS-III). Many of us have already got an account in the wiki, a bunch are following closely the evolution of one or more of the four surveys, BOSS, MARVELS, SEGUE-2 and APOGEE, through the mailing lists and the teleconferences, and there are even some who are already working actively on them. All this in a period of one year since the IAC´s participation was first proposed. In this seminar, we'll make a quick summary of the activities related to SDSS at the IAC, we'll present the latest news, and will make a live demonstration on how to access DR8 data.
Using the k-means cluster analysis algorithm, we carry out an unsupervised classification of all galaxy spectra in the seventh and final Sloan Digital Sky Survey data release (SDSS/DR7). Except for the shift to rest-frame wavelengths and the normalization to the g-band flux, no manipulation is applied to the original spectra. The algorithm guarantees that galaxies with similar spectra belong to the same class. We find that 99% of the galaxies can be assigned to only 17 major classes, with 11 additional minor classes including the remaining 1%. The classification is not unique since many galaxies appear in between classes; however, our rendering of the algorithm overcomes this weakness with a tool to identify borderline galaxies. Each class is characterized by a template spectrum, which is the average of all the spectra of the galaxies in the class. These low-noise template spectra vary smoothly and continuously along a sequence labeled from 0 to 27, from the reddest class to the bluest class. Our Automatic Spectroscopic K-means-based (ASK) classification separates galaxies in colors, with classes characteristic of the red sequence, the blue cloud, as well as the green valley. When red sequence galaxies and green valley galaxies present emission lines, they are characteristic of active galactic nucleus activity. Blue galaxy classes have emission lines corresponding to star formation regions. We find the expected correlation between spectroscopic class and Hubble type, but this relationship exhibits a high intrinsic scatter. Several potential uses of the ASK classification are identified and sketched, including fast determination of physical properties by interpolation, classes as templates in redshift determinations, and target selection in follow-up works (we find classes of Seyfert galaxies, green valley galaxies, as well as a significant number of outliers). The ASK classification is publicly accessible through various Web sites.
AbstractThe main goal of the MASTER-Net project is to produce a unique fast sky survey with all sky observed over a single night down to a limiting magnitude of 21. Such a survey will make it possible to address a number of fundamental problems: search for dark energy via the discovery and photometry of supernovae (including SNIa), search for exoplanets, microlensing effects, discovery of minor bodies in the Solar System, and space-junk monitoring. All MASTER telescopes can be guided by alerts, and we plan to observe prompt optical emission from gamma-ray bursts synchronously in several filters and in several polarization planes.
We present the new stellar population synthesis models based on the empirical stellar spectral library MILES, which can be regarded nowadays as standard in the field of stellar population studies. The synthetic SEDs cover the whole optical range at resolution 2.3 Å (FWHM). The unprecedented stellar parameter coverage of MILES allowed us to extend our model predictions from intermediate- to very-old age regimes, and the metallicity coverage from super-solar to [M/H] = -2.3. Observed spectra can be studied by means of full spectrum fitting or line-strengths. For the latter we propose a new Line Index System (LIS) to avoid the intrinsic uncertainties associated with the popular Lick/IDS system and provide more appropriate, uniform, spectral resolution. We present a web-page with a suite of on-line tools to facilitate the handling and transformation of the spectra. Online examples with practical applications to work with stellar spectra for a variety of instrumental setups will be shown. Furthermore we will also show examples of how to compute spectra and colors with varying instrumental setup, redshift and velocity dispersion for a suite of Star Formation Histories.
AbstractThe current databases of empirical star spectra for modelling single-aged stellar populations (SSPs) generally do not chemically characterize their stars completely. Spectral properties of stars and their populations may change considerably if the elemental abundance ratios E/Fe differ from the solar-scaled values. We intend to build up robust integrated spectral energy distribution of SSPs older than 1 Gyr by adopting the MILES database (Medium-resolution Isaac Newton Telescope Library of Empirical Spectra) and taking into account the Mg/Fe ratio of its stars. Magnesium is a proxy of the alpha-capture elements and the alpha/Fe ratio has been widely used as an indicator of the star formation time scale. In this talk, I present how accurate and extensive our compilation and determination of [Mg/Fe] were obtained around MILES to compute state-of-the-art SSP models. Published high resolution measurements were adopted to define a uniform scale of [Mg/Fe] and calibrate our results at medium resolution that were based on the spectral synthesis of two strong Mg features.
- Charla SMACKThursday July 1, 2021 - 10:30 GMT+1 (Aula)
- Análisis de stray light en instrumentación astrofísicaMiguel Ángel Cagigas GarcíaFriday July 2, 2021 - 12:00 GMT+1 (Aula)