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Spectroscopy surveys of stellar populations

Spectroscopy surveys of stellar populations. Danny Lennon (Isaac Newton Group & Instituto de Astrofisica de Canarias). Stellar Spectroscopy is now dealing with large scale surveys of stellar populations.

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Spectroscopy surveys of stellar populations

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  1. Spectroscopy surveys of stellar populations Danny Lennon (Isaac Newton Group & Instituto de Astrofisica de Canarias) Astronomical Spectroscopy & the VO

  2. Stellar Spectroscopy is now dealing with large scale surveys of stellar populations Multi-object spectroscopy is routine enabling us to tackle important scientific questions by investigating stellar populations rather than a few (special?) stars. Some of the issues will be illustrated with examples from: Spectroscopic follow-up of the one of the European Galactic Plane Surveys (EGAPS) : IPHAS. Astronomical Spectroscopy & the VO

  3. European Galactic Plane Surveys(EGAPS) • EGAPS is a loose association of Galactic Plane Surveys: • IPHAS – 300 million point sources Hα, r' and i' in the northern galactic plane (at the INT on La Palma); (70% passed data quality, 93% observed, DR1 coming soon) – www.iphas.org (J. Drew). • UVEX-N- u', g', and HeI5876 in north GP. Underway on the INT. (P. Groot) • VPHAS+ – 600 million point sources; southern plane counterparts of IPHAS & UVEX-N (awaits VST) (Drew & Groot) • IR surveys: UKIDSS-GPS & VVVetc (UKIRT & VISTA) (Lucas & Minniti) Astronomical Spectroscopy & the VO

  4. The INT Photometric Halpha Survey of the North Galactic Plane • Search and counts of all classes of Ha emitting stars/nebulae -short-lived but critical (birth, death, binarity, …) stages of stellar evolution: supergiants, LBVs, pre-MS, WR, Be stars, interacting binaries, PNe, HII regions, SNRs… • Study of Galactic structure (stellar populations, reddening), variables,… • Study of star-forming regions • etc Most of these objectives need spectroscopic follow-up Astronomical Spectroscopy & the VO

  5. Ha EW lower limit for normal stars The IPHAS colour-colour diagram. Drew et al. 2005 E(B-V)= r-Hα r-i Astronomical Spectroscopy & the VO

  6. The Spectroscopic follow-up: • Many telescope/spectrograph combinations and resolutions: • Multi-fiber: MMT/Hectospec (15,000) and WHT/AF2 (2,000) targeting all objects in the colour-colour plane using a customized selection algorithm • Plus numerous (~2,000) slit-spectra from WHT, INT, NOT, TNG, FAST, Calar Alto etc targeting specific object types in colour-colour plane • what about the information content…… Astronomical Spectroscopy & the VO

  7. Information content of stellar spectra • Hafner & Wehrse (1994, A&A, 282, 874) defined a quantitative method for estimating the information content of a stellar spectrum – the apparent spectral information (ASI) is based on the derivative of the flux with wavelength. • Example: • an AF2 spectrum has an ASI ~ 30 bits • riHα photometry has an ASI ~ 0.1 bits • Total ASI of present spectral data is ~0.6 Mbits and that of the photometric data is 30Mbits • Some examples of AF2 data… Astronomical Spectroscopy & the VO

  8. Deciphering the IPHAS colour-colour plane… green – emission line star bluetriangle – prominent Balmer absorption red cross – M star ....these ~2000 were classified by eye! Astronomical Spectroscopy & the VO

  9. A real task: Construct a 3D map of Galactic structure using A-type stars • Select all A-type candidates from their distinctive strip in the colour-colour plane (not a selection based on emission!) • Observe all candidates (several tens of thousands) • Classify all stars to spectral sub-type accuracy and luminosity class • Derive extinctions using intrinsic versus observed colour • Measure all radial velocities • Derive Balmer line equivalent widths and hence absolute magnitudes • Combine with photometry and astrometry to produce 3D distribution of A-type stars in Galaxy, and their radial velocities. Astronomical Spectroscopy & the VO

  10. What are the issues? • Need an automatic method of classification taking into account: • Variable extinction • Different wavelength ranges and resolutions • Variable s/n (a cruder reference frame at low s/n?) • Ignoring artifacts (e.g. badly corrected sky lines) • Find rare (‘easy’) objects. • Deliver radial velocities • Measure quantities • ..and physical parameters? • interface with model grids • and/or directly with codes (Genetic Algorithms) Astronomical Spectroscopy & the VO

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