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

2. 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

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) – (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

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

5. 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

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

9. 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

10. 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

11. 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