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

Astronomical Spectroscopy & the VO 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

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 & VVV etc (UKIRT & VISTA) (Lucas & Minniti) Astronomical Spectroscopy & the VO

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 Short-lived = rare Special directions like anticentre Most of these objectives need spectroscopic follow-up Astronomical Spectroscopy & the VO

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

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

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

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

Astronomical Spectroscopy & the VO 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

Astronomical Spectroscopy & the VO 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