Galactic Surveys Astrometry and photometry. Carlos Allende Prieto IAC

Transcription

1 Galactic Surveys Astrometry and photometry Carlos Allende Prieto IAC

2 Overview Astronometry: Hipparcos and Gaia Photometry: DSS, SDSS, 2MASS Fitting data to models Tuesday, August 27, 2013

3 Basic astronomical measurements (from light) Astrometry > positions of stars in the sky, proper motions, parallaxes Photometry > colors and brightness (stellar properties) Spectroscopy > radial velocities, line strengths, stellar properties

4 Gaia s Three Elements Astrometry (V < 20) completeness to 20 mag 109 stars accuracy: µarcsec at 15 mag scanning satellite, two viewing directions principles: global astrometric reduction (as for Hipparcos) Photometry (V < 20) Low-dispersion spectrophotometry µm Radial velocity (V < 16 17) slitless spectroscopy near Ca II triplet ( nm) third component of space motion, dynamics, population studies, binaries spectra: chemistry, rotation

5 Astrometry Positions and motions of stars provide full 3D maps of the near universe around us first the solar neighborhood, now more distant parts of the Milky Way and even the nearest local group galaxies First parallax measured in 1838 by Bessel (61 Cygni, 0.3 arcsec) The Hipparcos mission measured parallaxes for 1e5 stars with mas precision and 1e6 stars with lower precision between 1989 and Gaia is Hipparcos successor, with all-around Tuesday, August 27, enhancements 2013

6 Gaia: Complete, Faint, Accurate Hipparcos Gaia Magnitude limit Completeness Bright limit Number of objects Effective distance limit Quasars Galaxies Accuracy 1 kpc None None 1 milliarcsec Photometry photometry 2-colour (B and V) 20 mag 20 mag 6 mag 26 million to V = million to V = million to V = kpc 5 x µarcsec at V = µarcsec at V = µarcsec at V = 20 Low-res. spectra to V = 2

7 Stellar Astrophysics Parallaxes and photometry imply a comprehensive luminosity calibration distances to 1% for ~10 million stars to 2.5 kpc distances to 10% for ~100 million stars to 25 kpc parallax calibration of all distance indicators e.g. Cepheids and RR Lyrae to LMC/SMC accurate parallaxes imply accurate surface gravities and age

8 Stellar Astrophysics An unbiased survey implies a detailed Galactic census solar neighbourhood mass function and luminosity function e.g. white dwarfs (~200,000) and brown dwarfs (~50,000) initial mass and luminosity functions in star forming regions rare stellar types and rapid evolutionary phases in large numbers Statistics on variability across the board (~40 (RVS) (AS,XP) visits per object)

9 One Billion Stars in 6-d will Provide in our Galaxy the distance and velocity distributions of all stellar populations a rigorous framework for stellar structure and evolution theories a large-scale survey of extra-solar planets (~20,000) a large-scale survey of Solar System bodies (~ few 100,000) and beyond definitive distance standards out to the LMC/SMC rapid reaction alerts for supernovae and burst sources (~20,000) QSO detection, redshifts, microlensing structure (~500,000) fundamental quantities to unprecedented accuracy: γ to 10-7 (10-5 present)

10 Exo-Planets: Expected Discoveries Astrometric survey: monitoring of hundreds of thousands of FGK stars to ~200 pc detection limits: ~1MJ and P < 10 years masses, rather than lower limits (m sin i) multiple systems measurable, giving relative inclinations Π λαν τε : ρ = 100 µασ Π = 18 µοισ 1.2 δ( ) Results expected: ~20,000 exo-planets (~10 per day) 1 orbits for ~5000 systems 0.8 masses down to 10 MEarth to 10 pc 0.6 >1000 photometric transits 1 /0 7 /0 2 1 /0 1 /0 3 1 /0 7 / /0 7 / /0 1 /0 2 1 /0 1 /0 1 1 /0 1 / α χοσ δ ( ) 0.8 Figure courtesy François Mignard 1.0

11 Studies of the Solar System Asteroids etc.: deep and uniform (20 mag) detection of all moving objects ~ few 100,000 new objects expected (357,614 with orbits presently) taxonomy/mineralogical composition versus heliocentric distance diameters for ~1000, masses for ~100 orbits: 30 times better than present Trojan companions of Mars, Earth and Venus Kuiper Belt objects: ~300 to 20 mag (binarity, Plutinos) Near-Earth Objects: Amors, Apollos and Atens (2249, 2643, 406 known today) ~1600 Earth-crossers >1 km predicted (937 currently known) detection limit: m at 1 AU, depending on albedo

12 Satellite and System ESA-only mission Launch date: late 2013 Launcher: Soyuz Fregat Orbit: L2 Lifetime: 5 years Ground station: New Norcia and Cebreros Downlink rate: 4 8 Mbps Mass: 2120 kg (payload 700 kg) Power: 1720 W (payload 735 W) Figures courtesy EADS-Astrium

13 Tuesday, August 27, 2013

14 Payload

15 Payload and Telescope Two SiC primary mirrors m2 at Rotation axis (6 h) Basic angle monitoring system SiC toroidal structure (optical bench) Superposition of two Fields of View (FoV) Figure courtesy EADS-Astrium Combined focal plane (CCDs)

16 Figure courtesy Alex Short Focal Plane cm Wave Front Sensor 42.35cm Wave Front Sensor Basic Angle Monitor Bl ue P h ot o m et er C C D s Basic Angle Monitor R ed P h ot o m et er C C D s Radial-Velocity Spectrometer CCDs Star motion in 10 s Sky Mapper CCDs Total field: Astrometric Field CCDs Sky mapper: - detects all objects to 20 mag - active area: 0.75 deg2 - rejects cosmic-ray events - CCDs: FoV discrimination x 1966 pixels (TDI) - pixel size = 10 µm x 30 µm Astrometry: = 59 mas x 177 mas - total detection noise: ~6 e- Photometry: - spectro-photometer - blue and red CCDs Spectroscopy: - high-resolution spectra - red CCDs

17 On-Board Object Detection Requirements: unbiased sky sampling (mag, colour, resolution) all-sky catalogue at Gaia resolution (0.1 arcsec) to V~20 Solution: on-board detection: good detection efficiency to V~21 mag FPA CCDs generate Gbps thus windows needed

18 Sky Scanning Principle 45o Spin axis Scan rate: Spin period: Figure courtesy Karen O Flaherty 45o to Sun 60 arcsec/s 6 hours

19 Astrometric Data Reduction Principles Scan width: 0.7 Sky scans (highest accuracy along scan) Figure courtesy Michael Perryman 1. Object matching in successive scans 2. Attitude and calibrations are updated 3. Objects positions etc. are solved 4. Higher terms are solved 5. More scans are added 6. System is iterated

20 Light Bending in Solar System Light bending in microarcsec, after subtraction of the much larger effect by the Sun Movie courtesy Jos de Bruijne

21 Gaia imaging 91 CCDs (4000 x 2000 pixels each) Distances for sources!

22 The Radial Velocity Spectrometer TDI spectroscopy!

23 Stellar motions

24 Photometry Measurement Concept Blue photometer: nm Red photometer: nm Figures courtesy EADS-Astrium

25 Photometry Measurement Concept Blue photometer wavelength (nm) wavelength (nm) Red photometer AL pixels spectral dispersion per pixel (nm) AL pixels RP spectrum of M dwarf (V=17.3) Red box: data sent to ground White contour: sky-background level Colour coding: signal intensity Figures courtesy Anthony Brown spectral dispe

26 Ideal tests Shot, electronics (readout) noise Synthetic spectra Logg fixed (parallaxes will constrain luminosity) G=18.5 G=20 Bailer-Jones 2009 GAIA-C8-TN-MPIA-CBJ-043 S/N per pixel

27 (Spectro-)photometry ILLIUM algorithm (Bailer-Jones 2008). Dwarfs: G=15 ([Fe/H])=0.21 (Teff)/Teff=0.005 G=18.5 ([Fe/H])=0.42 (Teff)/Teff=0.008 G=20 ([Fe/H])=1.14 (Teff)/Teff=0.021 G=20

28 RVS S/N ( per transit and ccd) 3 window types: G<7, 7<G<10 (R=11,500), G>10 (R~4500) (S + rdn2) Most of the time RVS is working with S/N<1 End of mission spectra will have S/N > 10x higher G magnitude Allende Prieto 2009, GAIA-C6-SP-MSSL-CAP-003

29 Sample RVS spectra (mission end, black line) G=10.5 G=12.3 G=15.8 B5V G2V Metalpoor K1III

30 RVS produce Radial velocities down to V~17 (108 stars) Atmospheric parameters (including overall metallicity) down to V~ (several 106 stars) Chemical abundances for several elements down to V~12-13 (few 106 stars) Extinction (DIB at nm) down to V~13 (e.g. Munari et al. 2008) ~ 40 transits will identify a large number of new spectroscopic binaries with periods < 15 yr (CU4, CU6, CU8)

31 RV performance Spec. for late-type stars 1 km/s at V<13 15 km/s down to V=17

32 Atmospheric parameters tests) Solid: absolute flux Dashed: absolute flux, systematic errors (S/N=1/20) Dash-dotted: relative flux Allende Prieto (2008) (Ideal

33 Photometry Gaia will not be the first full-sky photometric survey Palomar photographic plates (POSS) HST needed a full-sky pointing catalog, which was prepared from digitized photographic plates (DSS) 2MASS: first full-sky ground-based near-ir photographic survey (J H Ks filters) SDSS provided a large/area (14,000 sqr. deg) optical survey (ugriz system) using CCD Tuesday, August 27, 2013detectors

34 Usual photometric systems Johnson (-Cousins) UBVRI Ströngrem ubvy Near-IR Y J H Ks SDSS ugriz GALEX FUV/NUV System responses usually include (approximate) atmospheric extinction Tuesday, August 27, 2013

35 SDSS First massive solid-state optical photometric survey (some 14,000 deg2 and 150 million stars down to r ~ 22 mag) 2% photometry 1% in stripe 82 Highly-uniform observations (single site/telescope/instrument) Carefully designed filters (though issues with u-band) Tuesday, August 27, 2013

36 SDSS imaging 6 x 5 CCDs Running in TDI

37 The world s biggest picture 26 Gigapixels!

38 2MASS 2 automated 1.3m telescopes (one in Arizona, one in Cerro Tololo, Chile) 3 channel (J, H, Ks) cameras, each with a 256x256 HgCdTe detector 7.8s exposures 4 years of operation PSC: ~ 300 million stars down to J/H/Ks of ~ 16,15,14 About 1 million extended sources Tuesday, August 27, 2013

39 Tuesday, August 27, 2013

40 UKIDSS started in 2005 some 400 papers already published uses WFCAM on 4-m class UKIRT (four 2048x2048 Rockwell devices) 7500 sqr. Deg down to K~18 Tuesday, August 27, 2013

41 VHS 19,000 sqrt. deg About 4 mag. deeper than 2MASS Using ESO s VISTA telescope Tuesday, August 27, 2013

42 The Future: LSST A wide-field 8.4m telescope A 3.2 Gpix camera Imaging the whole (accessible sky) every few nights Starting in 2018 Tens of TB of data each night Tuesday, August 27, 2013

43 LSST

44 The variable sky Most of the transients are fairly near, but most exciting ones are far away

45 The variable sky

46 The variable sky We do not know what is out there Lots of room for classification algorithms

47 Zero-point Absolute calibration of astronomical sources is non-trivial Good lab reference sources hard to observe through telescopes as if they were at infinity Atmospheric extinction/distortion gets in the way Traditional reference source is Vega, which sets zero-point tied to lab sources (Tungsten lamps or black bodies; see Hayes 1985, Megessier 1995), but Vega is not easy to model Tuesday, August 27, Spectrophotometric calibration nowadays tied 2013

48 White dwarfs DA white dwarfs are fairly simple: just two parameters (Teff,logg), pure-h physics, NLTE but good agreement among models Examples From SDSS Allende Prieto, Hubeny & Smith 2009

49 HST DAs 3 DA white dwarf stars constitute the basis for HST calibration (see papers by Bohlin) Good to 1-2% Calibration consistent for Vega V= / Allende Prieto, Hubeny & Smith 2009

50 HST DAs analyzed with different models Allende Prieto, Hubeny & Smith 2009

51 A-type stars Not pure hydrogen, but spectrum dominated by it in optical and IR (continuum and lines); exception FeII lines in UV Three parameters (Teff,logg,[Fe/H]) Reddening needs to be accounted for (also true for faint WDs) Brighter and more common than WDs

52 A-type stars Not pure hydrogen, but spectrum dominated by it in optical and IR (continuum and lines) Three parameters (Teff,logg,[Fe/H]) Reddening needs to be accounted for (also true for faint WDs) Brighter and more common than WDs Allende Prieto & del Burgo (in prep). Spectra from NGS (Gregg et al.)

53 Vega Fast rotation Allende Prieto & del Burgo (in prep). HST spectrum Gilliland & Bohlin

54 Zero-point HST flux calibration: using zero-point V magnitude for Vega (not quite zero, V= mag) and 3 DA WDs models Vega STIS spectrophotometry calibrated in that way compares well with a model atmosphere for Vega and leads to a consistent zero-point based on photometry performed on the model System seems robust to 1-2% level STIS spectrophotometry (calspec, NGSL) now Tuesday, August 27, being used to set zero points for photometric 2013

55 Halo turn-off stars F-type, metal-poor: H continuum + lines and few metal lines (not so few in the blue/uv) Again 3 parameters (+ reddning) but now higher impact of [Fe/H] due to electrons forming HMany of them (just leaving the main sequence), easy to pick up from colors Choice used for SDSS BD is the prototype

56 Halo turn-off stars F-type, metal-poor: continuum H and H-, H lines and few metal lines (not so few in the blue/uv) Many of them (just leaving the main sequence), easy to pick up from colors Choice used for SDSS BD is the prototype Ramírez et al. 2009; HST data from Bohlin and colleagues

57 Fitting models to data Understanding the structure of the Milky Way is critical Starcounts are the most fundamental (and easy) measurement: just photometry and coarse astrometry (star positions) Distances must be estimated, but parallaxes to a few percent available for only some 1e5 stars (Hipparcos) Photometric parallaxes derived for dwarfs based on models or semi-empirical Tuesday, August 27, relationships (e.g. clusters) 2013

58 Color absolute mag relationships for dwarfs Tuesday, August 27, 2013 Juric et al. 2008

59 Standard candles Dwarfs outnumber giants in most cases (not always). Their luminosities depend on metal content but weak dependence on age at a given color An alternative is to use stars at specific evolutionary stages that can be identified with certainty, and with reliable theoretical (or semi-empirical) luminosities Examples include cepheids, red-clump stars, RR Lyrae Tuesday, August 27, 2013

60 Standard candles For example, red-clump giants have been very useful in the obscured parts of the Milky Way An approximate extinction relation between colors and passbands can be adopted Cabrera-Lavers et al Tuesday, 27, 2005 BabuiauxAugust and Gilmore 2013

61 Red-clumb giants in the bulge Cabrera-Lavers et al Tuesday, August 27, 2013

62 Large data sets One can either fit the data with models, e.g. Larsen & Humphreys (2003), Robin et al. (2003) Or derive density maps, which are subsequently fit to infer the model parameters, e.g. Juric et al Models involve a number of std. Milky Way stellar components: a disk (or two), a halo, and a bulge (plus other non-std. such as a bar or streams as needed) Tuesday, August 27, more complex orbit-family-type or Nowadays, 2013 numerical-simulations available, but

63 Density maps Photometric parallaxes are derived first Positions on the sky and distances are used to create a binned density map (Juric et al. 2008) Photometric [Fe/H] estimates can be used Tuesday, August 27, 2013

64 Density maps This approach allows to clean-up the density maps before we fit radially symmetric models Juric et al Tuesday, August 27, 2013

65 Fitting models to data Typical 3-4 component stellar Milky Way models involve 6-8 parameters: relative densities, halo exponent, disk scale height(s) and length(s) Extinction needs to be included in disk and bulge Parameters constrained by optimization algorithm algorithm Tuesday, August 27, 2013

66 Tools Besançon model (Gaia universe model) M. Cohen s model TRILEGAL (see Girardi s lectures) GALFAST (Juric) Jordi Molgo s simulator Tuesday, August 27, 2013

67 What s next Back to Gaia Starcounts soon to be suplemented with trig. Parallaxes (replacing photometric ones) and spectrophotometric metallicities (Gaia) plus spectroscopic metallicities and more detailed abundances for a fraction of the sample (APOGEE/SDSS, Gaia-ESO, GALAH ) Further work on map construction desirable Idem for tools for evaluating simple, parametric, Milky Way models Tuesday, August 27, 2013