Gaia-ESO and IPHAS/VPHAS+
 A talk by Geert Barentsen for the Gaia-ESO workshop in Palermo, 21 May 2014 Image: ESO/VPHAS+ 

Hi. I am Geert [ɣeːrt], a postdoc in Hertfordshire (UK) @GeertMcTwit www.geert.io
 github.com/barentsen
 

! ! VPHAS+, IPHAS and UVEX are
 imaging the entire Plane & Bulge
 in ugriHα down to ~21st mag
 at 0.7-1.1” median seeing. ! I will tell you about: 1. survey progress and cluster coverage; 2. how the data complement GES; 3. our new data releases. Summary 

Core functions:
 University of Hertfordshire (VPHAS+/IPHAS PI) University of Nijmegen (UVEX PI) University of Cambridge (CASU pipeline) ! Other members include: IAC, University of Graz, Warwick University, University College London, Tautenburg Observatory, University of Graz, University of Bristol, University of Exeter, Imperial College London, University of Manchester, Southampton University, Armagh Observatory, Macquarie University, Harvard-Smithsonian CfA, ESO, University of Valencia. ! Key individuals include: Janet Drew (PI), Paul Groot (UVEX lead), Romano Corradi, Jochen Eisloeffel, Hywel Farnhill, Boris Gaensicke, Robert Greimel, Eduardo Gonzalez-Solares, Mike Irwin, Danny Steeghs. The collaboration 

Survey design and progress 

32-CCD OmegaCAM VLT Survey Telescope (Paranal) VPHAS+ is short for “the VST Photometric Hα Survey
 of the Southern Galactic Plane & Bulge” 

Image: ESO/S. Brunier 

300 310 320 330 340 350 0 10 20 30 40 10 5 0 5 10 Phase 2 submitted Awaiting submission 200 210 220 230 240 250 260 270 280 290 300 Galactic longitude (l) 10 5 0 5 10 Galactic latitude (b) VPHAS+ is observing 2269 fields, each covering ~1 deg2. GES clusters were deliberately scheduled early. Young clusters already covered include NGC3293, NGC3766 , NGC6231, NGC6405, NGC6530, NGC6611, Tr14-16, Tr24, IC2944, IC2602 (partial) + many old OCs. 

g r u i Hα Pattern of VPHAS+ data-taking ‣ Red (Hα, r, i) concatenations: 
 3 fields x (3x120, 2x25, 2x25 sec) ‣ Blue (u, g, r) concatenations: 
 3 fields x (2x150, 3x40, 2x25 sec) ‣ 5σ limiting (Vega) magnitude = ~21 mag Hα filter 

Lagoon Nebula (~1.5º wide) 1.25 kpc, ~2-3 Myr
 Credit: ESO/VPHAS+ 

NGC 3324 & NGC 3293 (r+i+Hα, 1.5º wide) 2.3 kpc, ~10 Myr
 Credit: H. Farnhill 

NGC 3293 (Hα, 5’ wide) NB: VPHAS+ saturates near ~13th magnitude 

NGC 3766 (Hα, 1.5º wide) 1.5 kpc, ~14 Myr 

NGC 3766 (Hα, 10’ wide) 

IC 2944 (Hα, 40’ wide) 1.8 kpc, ~7 Myr? 

IC 2944 (Hα, 3’ wide) 

IC 2944 (Hα, 1’ wide) 

Trumpler 14 (Hα, 6’ wide) 2.7 kpc, ~6 Myr
 (cf. Ronny Blomme’s talk?) 

Trumpler 16 (Hα, 6’ wide) 

eta Car (Hα, 1.5’ wide) (NB: this probably looks better in the i band) 

NGC 6611 (Hα, 20’ wide) 1.75 kpc, ~1-3 Myr
 (cf. Sarah Bonito’s talk) 

NGC 6611 (Hα, 2’ wide) 

Westerlund 1 (g+i+Hα, 10’ wide) 3-5 kpc, ~4 Myr?
 Credit: N. Wright 

“The Ionized Nebula surrounding the Red Supergiant W26 in Westerlund 1” (Wright et al. 2014, MNRAS) VPHAS Hα image 

VPHAS+ PSF FWHM 
 Filter Q10 median Q90 
 
 u 0.74” 0.97” 1.19”
 g 0.63” 0.83” 1.05”
 r 0.56” 0.76” 0.98”
 
 Hα 0.61” 0.82” 1.15” 
 r 0.61” 0.80” 1.10”
 i 0.56” 0.74” 1.05”
 
 

VPHAS+ depth ‣ Typical 5-sigma limits (Vega): 21 (u, Hα, i), 21.5 (r), 22.5 (g) ‣ log(source counts / sq. deg) across the 5 bands in single exposures: g, Hα, r, i u (NB: u-band exposure time chosen to capture u-excess objects) 

300 310 320 330 340 350 0 10 20 30 40 10 5 0 5 10 u,g,r and H↵,r,i observed u,g,r observed H↵,r,i observed Awaiting observation 200 210 220 230 240 250 260 270 280 290 300 Galactic longitude (l) 10 5 0 5 10 Galactic latitude (b) VPHAS+ completion rate (up to end March 2014): ‣ Red filters: 779 fields (34%) ‣ Blue filters: 480 fields (21%) ‣ All filters: 447 fields (20%) 

Wide Field Camera Isaac Newton Telescope (La Palma) The INT Photometric Hα Survey
 of the Northern Galactic Plane The UltraViolet Excess Survey
 of the Northern Galactic Plane 

Image: Nick Risinger 

r i Hα ‣ Northern equivalent of VPHAS+ (Hα, r, i) concatenations:
 1 field x (2x120, 2x30, 2x10 sec) ‣ Started in 2003 and now >92% complete;
 IPHAS DR2 submitted to MNRAS last month. 

U g r ‣ Mirrors the VPHAS+ (u, g, r) concats:
 1 field x (2x120, 2x30, 2x30 sec) ‣ Started in 2006, nearly caught up with IPHAS now. 

IPHAS has successfully observed ~7000 fields (92%) ‣ each covering 0.3 deg2; ‣ median PSF FWHM = 1.1”; median 5-sig depth = 21.2 (r), 20.0 (i), 20.3 (Ha); ‣ new data release to be detailed at the end of this talk. 

So, why should you care? 

Wide-area optical photometry 
 complements GES in several ways ! ‣ The data is homogeneous: one instrument, one magnitude system, one calibration. ‣ Obvious applications: ‣ the data enables target selection across wide areas; ‣ globally calibrated magnitudes enable luminosities (and ~ages) to be estimated in a uniform way across clusters; ‣ Hα images provide context (e.g. cometary globules, ionised rims, outflows); ‣ Hα photometry reveals emission-line objects (e.g. useful to understand the completeness of a GES sample with respect to accreting stars).
 ‣ Specialist applications: ‣ (r-Hα) is a proxy for the intrinsic stellar colour => 3D extinction maps; ‣ the u-g, g-r diagram reveals new OB stars; ‣ Hα images can inform sky background subtraction (to some extent). 

Examples of relevant applications 

AV = 5 r-i, r-Hα diagram (NB: the g-i, r-Hα diagram is even more powerful) 

IC 1396 in IPHAS (r+i+Hα, 4º wide) O6V-type
 ionising star 

IPHAS r, i, Hα photometry led to the discovery of 124 new classical T Tauri stars in IC 1396 Empirical boundary of chromospheric activity from (Barrado Navascues & Martin 2003) r - Hα r - i (Barentsen et al. 2011) 

Many of the T Tauri stars in IC 1396 were found clustered in front of star-forming cometary globules (Barentsen et al. 2011) 

O6V-type
 ionising star IC 1396 may show an evolutionary (age?) gradient away from the most massive star Class 0/I YSOs T Tauri stars (Barentsen et al. 2011) 

Close-up of IC 1396 A (r+i+Hα, 1º wide) Credit: Nick Wright 

IC 1396 may show an evolutionary (age?) gradient away from the most massive star O6V-type
 ionising star Class 0/I YSOs T Tauri stars (Barentsen et al. 2011) 

T Tauri candidates in IC 1396 using I Figure 4. IPHAS colours of known T Tauri stars in IC 1396 from Sicilia-Aguilar et al. (2005). Green squares are classical T Tauri stars (CTTS) with spectroscopic EWH↵ stronger than - 10 ˚ A. Red triangles are weak-line T Tauri stars (WTTS) with EWH↵ weaker than -10 ˚ A. The solid line shows the simulated main sequence curve at the mean reddening of the cluster ( ¯ AV = 1.56). Dashed lines shows the position of stars at increasing levels of H↵ emission as predicted by our simulated tracks. Grey dots show field stars in the region. The arrow shows the reddening shift for an M0V-type object being reddened from AV = 0 to AV = 1.56 (note that the true reddening tracks are curved in a is the typical reddening found by SA05). W the classical T Tauri stars are well separated stars (shown as grey points): most are abo EW boundary as predicted by the drawn grid trast the weak-lined stars fall within the mai blending in with normal less-reddened stars. reddening raises the EW threshold for the c of emission line stars is a recognised property colour-colour plane (see Drew et al. 2005). One weak-lined object, named 73-537 in seen to fall somewhat below the simulated (solid line in Fig. 4). The aberrant position i the high reddening of the object, AV = 3. outlier in terms of reddening compared to t sample. To validate the grid in more detail, we in tracks to derive H↵ EWs for the known T These values are then plotted against the spe ues from SA05. The comparison is shown in F a strong correlation between the photometri scopic estimates, albeit with a large scatter o 5 to 10 ˚ A. Figure 4. IPHAS colours of known T Tauri stars in IC 1396 from Sicilia-Aguilar et al. (2005). Green squares are classical T Tauri stars (CTTS) with spectroscopic EWH↵ stronger than - 10 ˚ A. Red triangles are weak-line T Tauri stars (WTTS) with EWH↵ weaker than -10 ˚ A. The solid line shows the simulated main sequence curve at the mean reddening of the cluster ( ¯ AV = 1.56). Dashed lines shows the position of stars at increasing levels of H↵ emission as predicted by our simulated tracks. Grey dots show field stars in the region. The arrow shows the reddening shift for an M0V-type object being reddened from AV = 0 to AV = 1.56 (note that the true reddening tracks are curved in a way that depends on the SED and the amount of reddening, see Drew et al. 2005) -1 -10 -100 Spectroscopic EW [ ˚ A] -1 -10 -100 IPHAS Photometric EW [ ˚ A] Figure 5. Comparison of IPHAS photometric EWH↵ with spec- troscopic values from Sicilia-Aguilar et al. (2005). The grey dashed line shows the unity relation. The scatter is thought to Hα magnitudes, when combined with the broadbands, can provide a handle on the Hα EWs: Validation against low-resolution spectroscopy from (Sicilia-Aguilar et al. 2005): (Barentsen et al 2011) 

However, parameter-space degeneracies can be important when data is sparse e.g. extinction vs Hα EW degeneracy: Also: distance-vs-age degeneracy, extinction-vs-mass … 

Mass Mass Age Extinction To understand parameter-space degeneracies, one should compute the full posteriors (e.g. using MCMC) P(Mass, Extinction | Data) P(Mass, Age | Data) For example, the posterior for a ~20th magnitude T Tauri star in NGC 2264: 

Defining a multi-dimensional posterior can be made easy using probabilistic graphical models (PGMs): (Barentsen et al. 2013) 

The use of PGMs and MCMC for inferring T Tauri star parameters is explained in (Barentsen et al. 2013) (NB: this works for spectra too) => applied to all known 
 members of NGC 2264
 using IPHAS data 

Other applications 

(Mohr-Smith et al, in prep) New OB-star candidates can be identified using the u-g, g-r diagram 

OB star parameters (Teff, μ, A0, Rv) can be inferred from ugriJHK data using MCMC Typical uncertainty on A0 and Rv is ~0.1 across the magnitude range. ! (Mohr-Smith et al, in prep) 

0.0 0.5 1.0 1.5 2.0 2.5 3.0 r - i 12 13 14 15 16 17 18 19 20 r 0.0 0.5 1.0 1.5 2.0 2.5 3.0 r - i 12 13 14 15 16 17 18 19 20 r E(B-V)=1 E(B-V)=2 E(B-V)=3 Optical/NIR photometry offers a handle on the properties of the population and the extinction along a line of sight l = 180 deg (anti-centre) l = 45 deg e.g. colour-magnitude diagrams towards two different sight-lines: 

2005MNRAS.362..753D (Drew et al. 2005) Main sequence Reddening In particular, (r - Hα) is a coarse proxy for spectral type, and is less sensitive to reddening than broadband colours 

IPHAS DR2 northern Galactic Plane extinction map derived from r, i, Hα using MCMC (Sale et al, submitted) Galactic longitude Extinction
 (mag) (Angular resolution:~10 arcmin) 

Hα images provide a spatial view 
 of the sky background intensities ‣ Note that the sky fluxes are not calibrated in an absolute sense; you can only use them in a relative sense within coeval exposures. ‣ Subtracting the background can be a conundrum for photometry as well. Problematic cases are flagged in our catalogues, for example: IPHAS Hα image (30 arcsec wide) 

Data releases 

The new IPHAS data release ‣ The IPHAS DR2 Source Catalogue was submitted to MNRAS last month ‣ 219 million unique sources,
 globally calibrated to 0.03 mag accuracy; ‣ accompanied by a 3D extinction map, and probabilistic 
 (μ, A0, Teff, logg, Mass) estimates for 38 million stars. ‣ Catalogue to be made available through iphas.org and CDS/Vizier. ‣ All pipeline-reduced images will also be downloadable from 
 iphas.org once the paper is accepted. 

Ongoing VPHAS+ data releases ‣ Raw data is available in the ESO archive straight away. ‣ Pipeline-reduced images and single-band catalogues are delivered to the ESO archive in ~annual releases (DR1 April 2013; DR2 June 2014). ‣ Work has started on a globally-calibrated source catalogue, building on the experience gained with IPHAS. ‣ Talk to us to obtain preview catalogues.
 
 Keep an eye on our website: http://www.vphas.eu 

Conclusions ! ‣ The VPHAS+/IPHAS/UVEX surveys complement GES with optical photometry down to ~21st magnitude. ‣ u- and Hα-band sensitivity, along with the excellent PSF quality, are the unique strengths. ‣ High-res Hα images provide contextual information on the morphology of star-forming regions. ‣ Major data releases are happening right now. 

Thank you