SkyMapper

1. Brian Schmidt, Mike Bessell, Stefan Keller, Patrick Tisserand, Gary Da Costa and Paul Francis SkyMapper

2. 1.35m telescope with a 5.7 sq. degree field of view Fully Autonomous observing To conduct the Southern Sky Survey: Five year Multi-colour (6 filters) Multi-epoch (6 exposures, each filter) 2π steradians Limiting mag. g~23 Aiming for regular operations this year Summary of program: Keller et al. 2007 PASA 24,1 What is SkyMapper? Total Cost: Hardware US$11M oftware: ~$1.5M Dedicated Science/Operations: ~0.6M/yr Slide

3. The SkyMapper Telescope

4. Telescope Optics 0.75m secondary 0.6m fused silica asphere 1.3m primary 2 x 0.45m fused silica spherics

5. 6 Filter slots (< 10 second exchange time) Bonn shutter (2ms accuracy) Exposure homogeneity <0.3% at 0.1sec 32 E2V CCD44-82 devices: 2048x4096 15 micron pixel CCDs Broadband coated 40 micron (thick) devices Reduced fringing, inc. red response, without bad blue 16384x163840.5” pixels Using new Pan Starrs controllers (Onaka at IfA) Readout in ~20 seconds through 64 64 channels (300 kpix/s) Readnoise ~7e The SkyMapper imager and CCDs

6. 2π coverage: shallow survey. Photometric and astrometric Calibration of the Southern Sky in 6-filters (3-epochs per colour) 2π coverage: ~4000 fields observed in six filters, six times per filter to a (13-22 mag) Cadence: hours, days, weeks, months, years Photometry to 0.02(0.01 aspiration) mag globally (g>18.5) astrometry to 50 (15) mas 36 images of each object over 5 years ⇒ proper motions to ±5(2) mas/yr. (i.e. σvtan=25km/s at 2.5(6) kpc) ⇒ parallax ±5(2) mas (i.e. 20pc (50) σd=10%) survey complete in 5 years using 75% of telescope time The Southern Sky Survey(>=75% of all available time)

7. moon

8. T, log(g), and Z are encoded in the spectrum of each star Using filters we can isolate portions of the spectrum In designing our survey we sought to optimise our ability to determine the three important stellar parameters (T,log(g), Z) so SkyMapper not only complements survey efforts in the northern hemisphere but enables us to tackle important astrophysics in an exciting new way. SkyMapper Optimised for Stellar Astrophysics but SN program driver for precision photometry Bessell et al. 2011 PASP 123, 789

9. Expected Main Survey limits AB mag. for signal-to-noise = 5 from 110s exposures

10. 1st epoch : all filters consecutively (colour + short term variability in uv) 3 first epochs in (g,r) in less than 7 days : for Astrometric and photometric short term variation (TNO + RR Lyrae/Cepheids+young SN): (i,z) spread out to measure parallax over the year. in total, 160,000 sq-degrees observed per year to g~22 Use a “Score” algorithm for field priority - weighted by amount of time field is observable in survey’s remaining time. Deal with “Quick Data Quality Check” + Database Quality to validate each field meets criteria to be in main survey. Take care : distance of the Moon, Planets, Sky conditions, Satellites... Cadence

11. Conduct Shallow Survey in mainly photometric conditions cover the southern sky with 3 x (30, 30, 5, 5, 10, 15) exposures: 12-17th mag primary standards: Seven new STIS spectrophotometric stds 0.3 sec exposure for ~9 mag standards During shallow survey observe the highest two reference fields every 90 minutes Anchor the deeper Main Survey to the Shallow Survey photometry and astrometry Enables the Main Survey to proceed under non-photometric conditions. Self Calibration via overlaps and the Main sequence (in low dust areas) Calibration Plans

12. Calibration procedures following Regnault et al. (2009) A&A 506, 999 for MegaCam on CFHT. Bias subtraction, linearity correction Flat fielding, scattered light and fringe removal 1) generate median twilight flatfields in all colors 2) generate superflats from median filtering only night-sky pixels 3) subtract scaled twilight flat from superflat to give fringe flats in I and z 4) scale and subtract fringe frame from observations 5) generate true flatfield by dithering standard fields in 8 offsets NS and 8 offsets EW.This to be done every ~6 months. Use SkyDICE to monitor mirror reflectivity and filter transmission ~daily. Clean mirror when advised. Calibration strategy

13. System of direct illumination Calibrated Photodiodes (NIST) 25 – 30 LEDs 3000 – 11000Å Precision of 0.1% between 4000 and 9000Å Monitoring instrument ~0.01% Permanently mounted on dome Nicolas Regnault - LPNHE SkyDICE

14. During commissioning establish a series of photometric reference fields around the sky. DDT application will be made for 15 STIS spectra to be measured to <1% precision 3000Å – 10200Å Fields will be centered on 7 southern STIS stds Six fields at 4 hour intervals between -18S and -49S. One at -87S to ensure pole region well calibrated. These fields will provide calibrated photometry over the entire SkyMapper field of view. + Six northern SDSS stds and 3 equatorial stds. Photometric reference fields

15. Need for precise spectrophotometry Our goal is to tie photometry in both hemisphere to an absolute spectrophotometric system - This would serve the basis of SkyMapper's photometric system, and is the basis of the calibrations necessary to undertake supernova cosmology experiment to a high degree of precision. Currently, uncertainties in the overall calibration of SN to the fundamental standards is the largest single source of systematic uncertainty in the SN experiments. These data would be used for current SNLS/SDSSII work, as well as SkyMapper, and DECCAM, and eventually LSST calibration.

16. Problems with NGSL spectra Currently there are two spectrophotometric catalogs from HST - NGSL, and CALSPEC. We had hoped to use the NGSL objects as our fundamental standards - but it appears that due to slit effects, there remain uncertainties (~ 2%) in the relative flux as a function of lambda. Sally Heap will discuss the NGSL stars at this meeting. The CALSPEC stars, which used a wide slit and were well centered, do not suffer from this problem, but have other drawbacks that make the current ensemble difficult to use to achieve our goals

17. CALSPEC spectra drawbacks • Very few moderate colored stars which can be tied directly to normal stars in the survey. The very blue stars typically require extrapolation from the bulk of the objects we wish to calibrate. • There are no appropriate southern stars which we can use to tie down our 1/2 of the sky. • Very few stars that can currently be tied to an external photometric system (Hipparchos now but GAIA is coming). This provides an overall normalisation and homogenisation to the spectra - instead of simply relying on the fidelity of HST.

18. Choosing new secondary standards • It would be good to extend the HST calibrated stars to cover a wider color range of objects to ensure that bandpasses of our systems are correctly realised. • It is also important that the spectra can be well modeled so that accurate fluxes can be synthesized across a wide wavelength range. • It is generally accepted (eg. Bohlin) that hot DA white dwarfs are the best and most reliable to model, but the smooth spectrum and neutral colors of metal-poor FG-stars (subdwarfs), provide additional benefits and they also seem to be well modeled.

19. Southern STIS Spectrophotometry Name Hip RA2000 Dec2000 V/B-V Hp/err Te/logg [Fe/H]

20. Northern STIS Spectrophotometry Name Hip RA2000 Dec2000 V/B-V Hp/err Te/logg [Fe/H]

21. g~12 is the bright limit for 5 sec focussed exposures. This necessitates ~0.2 sec exposures for 8.5 mag or out-of-focus imaging. Scintillation at 0.2 sec is < 0.01 mag Shutter imprecision (0.2ms) and homogeneity (0.3% at 0.1 sec) should not be an issue. Issues with defocussing – curve of growth problems? Needs exploration. Useful to establish fainter spectrophotometric standards with ground-based telescopes (Tonry). Caveats

22. Determine photometric status of each night by performing aperture photometry of all point sources and compare with 2MASS color-magnitude relations. Observe two different standard reference fields every hour to provide zero-points for each chip and illumination correction. Calculate extinction and derive zeropoints. Monitor seeing, photometric zp, sky-background. Observe different passbands consecutively. Use SExtractor with aperture twice fwhm, then correct to infinite aperture, to generate standard magnitudes. The Shallow Survey

23. Shallow Survey Data to be acquired in photometric and non-photometric time.

24. Use stars from Shallow Survey to put instrumental photometry on the standard instrumental system. Combine images and create object catalog. At high galactic latitude do for all bands, at low use I band. Extract transients by comparing individual frame with combined frame, after masking out cataloged objects, and locating objects with appropriate PSF. Determine PSF shape for each object in each image in a filter. Use as basis for galaxy/star separation. Determine galaxy shape parameter (PA and ellipse isophot) and measure magnitudes (Source Extractor III). Main survey photometry

25. Before Magnier & Cuillandre (2004, PASP 116, 449) and Regnault et al. (2009 A&A, 506, 999) widefield photometry was not considered by many people to be capable of delivering better than 3% photometry. But we are all here this week discussing how to achieve 1% photometry. A paradigm shift. We thank all those who have worked to make this happen. Acknowledgements

26. The hexagonal structures that were visible in the middle and the corners have gone.The new flat is actually flat. Flats before and after

27. These features have completely disappeared thanks to the velvet tape stuck on the carbon fiber collar in front of the camera and the 10 mm wide ring painted on the outside of the 3rd CLA lens. Pinhole test - edge of field

28. Using the velvet tape on the inside of the CLA and secondary baffles, we have removed the bright lines due to the baffle junctions. Pinhole test - on axis The black disk placed in the middle of the secondary has been useful to eliminate the reflection of the secondary itself on the CLA lens.

29. Waffle pattern from laser annealing. Removed by flat fielding. Seen in u and v frames. Sample v filter sky flat

30. Satellite trails with cryocooler on and off. Seeing 2” when on. 1.3” when off. Telescope oscillation

32. SkyMapper Filter Set Ex-atmosphere Bessell et al 2011PASP 123, 789

33. Maximize the science output 1st epoch : all filters consecutively u,v,g,r,u,v,i,z,u,v (color + short term variability in uv. 3 first epochs in (g,r) in less than 7 days : for Astrometric and photometric short term variation (TNO + RRlyrae/Cepheids): (i,z) spread out parallax over the year. Use a “Score” algorithm for field priority - weighted by amount of time field is observable in survey’s remaining time. Deal with “Quick Data Quality Check” + ANUSF DataBase Quality to validate each field meets criteria to be in main survey. Take care : distance of the Moon + Planets, reduce Airmass.. Observational Scheduler • The scheduler must respond to photometric/seeing conditions during a night.

34. Some Science Themes • What is the distribution of large Solar-System objects beyond Neptune? • What is the history of the youngest stars in the Solar neighbourhood? • How far does the dark matter halo of our galaxy extend and what is its shape? • Gravity and metallicity for on order of 100 million stars  the assembly and chemical enrichment history of the bulge, thin/thick disk and halo? • Extremely metal poor stars. • Undiscovered members of the local group – Sculptor,Cen too… • accurate photometric calibration of galaxy redshift surveys: 2dF/6dF. • bright z>6 QSOs  probes of the ionization history of the Universe.

35. Structure of outer Halo of galaxy with giants, BHBs and RRs

36. Blue Horizontal Branch Stars A-type MS and BS BHBs

37. The SDSS technique Use a set of colour and spectroscopic indices to isolate BHBs Extend to 60kpc The SkyMapper technique Photometric BHB selection to 130kpc with 5% contamination + RRs obtained from time series …and lines of sight to HVCs Sagittarius stream Structure of outer Halo of galaxy with giants, BHBs and RRs From Sirko et al. 2004

38. Extremely Metal-poor Stars in the Halo • Goal: find the first stars to have formed in the Universe: tell us about the assembly and chemical enrichment of the Galaxy • v-g is dependent on the level of metal line blanketing in the blue continuum • not perturbed dramatically by C-enhancement, chromospheric emission as affects objective-prism surveys F G

39. Detection is simple: i-band dropouts. Contaminants: L+T dwarfs SDSS tells us we can expect of order 50 objects z<20.5 in the SSSS Detection limited by our i sensitivity (not z!) Proper motions can help remove most L+T dwarfs as will J,H,K photometry initial follow-up with WiFES+2.3m and IRIS2+AAT SkyMapper High-z QSOs

40. Chemical abundance measurements of individual stars to learn about SN yields, Pop-III stars?, and how smallest galaxies form. Search for extreme LSB MW satellitesJerjen, Willman, Mateo ... SkyMapper will cover an uncharted 20000 sq-degrees 0.7 mag deeper than SDSS. UMa, 100kpc, -6.8? Discovered by Willman et al. 2005 from SDSS data

41. All Sky Tully-Fisher peculiar velocity survey when combined with ASKAP (250000 galaxies) input catalog for HERMES (+Teff and g) QSOs (Bright QSOs for dz/dt, dα/dz, TPE) and input to Lyα-BAO experiment large sample of hyper-velocity stars in halo based on gravity+metallicity Transiting planet discrimination (HAT-South based at RSAA) Discovery of rare stars (e.g. R Cor Bor, AM CVn) SkyMapper And a whole lot more

42. Hα of Southern Sky Mg 5100 filter for K Giants (maybe not needed) GRB, Gravity Wave, Radio Transient TOOs SN Search override High Cadence Variability surveys up to 25% of time for other things

43. Poor Seeing Time Southern Sky Survey Time

44. Data Release • Deliverables to the Outside User: • Data (epoch, RA, DEC, mags, galaxy shape info,…) to be available through a web-served interface which provides catalogs over a user defined area • Images to be available through a web-served interface which provides images over a user defined area (1 degree max, cut out of a 2-degree TAN projection across the sky), or individual frames. • Data release will occur after extensive data validation: • Shallow survey data after closure in RA and trial application to concurrently obtained main-survey data • FDR Main Survey 3 epochs all filters • SDR Main Survey 6 epochs all filters

45. Non-ANU parties can gain access to data during data characterisation period: • Request is forwarded to Project Scientist for SkyMapper. Project Scientist will ensure Project does not overlap/interfere with existing projects. • Establish a memorandum of understanding (MOU) between the external investigators and the School regarding the usage of data for specific purposes and authorship policy (inclusion of SkyMapper Development Group). External groups will be expected to visit Stromlo (we will try to support) as part of the MOU.

46. Problems solved Scattered light in telescope - paint, masks, baffles Air-conditioners, dry air - more Fail-safe remote observing - new single board computer Gradient in bias - software Remaining problems M2 resonant vibration Currently 48 sec between exposure, aim is 30 sec. Read-noise is 7e on most CCDs. 100hz cryo-cooler induced resonance in M2 causes image wobble. Problems encountered

47. In operation for last 2 weeks. Still some issues with TAROS. Still working on a few CCDs. Dampers ordered. Current status

50. Nicolas Regnault & Julien Guy