for Astrometry in the 21st Century William van Altena

Transcription

1 The Opportunities and Challenges for Astrometry in the 21st Century William van Altena Yale University, New Haven, CT USA (With slides from Elliott Horch, Dana Casetti-Dinescu and Daniel Harbeck) ADeLA IV, Mexico, Feb. 12,

2 Astrometry and Technology Science opportunities and advances in astrometry are driven by technology Radio astrometry t arrays VERA and micro-arcsecond parallaxes of maser sources in young star forming regions now available! Hipparcos & HST Fine Guidance Sensors The Solar neighborhood SIM, Gaia and OBSS The Milky Way and the Local Group VLTI, Keck I, CHARA, NPOI Star formation and stellar astrophysics ADeLA IV, Mexico, Feb. 12,

3 Positional accuracy Astrometric accuracy evolves Technology Parallax Proper Motion Limitations 2 mas WIYN I-band & 660 uas 540 uas/y V, I < 20; 26 obs.; now OT CCD fwhm = mas WIYN Z-band 330 uas 270 uas/y Z < 22; fwhm = 2010 & OTA CCD obs., four obs. 2 yrs later 6 uas Gaia V < uas 11 uas/y Mission i accuracy; 2020 V < uas 145 uas/y sigma = f(mag) 4 uas SIM V < 20, 15d 4 uas uas/yr Mission accuracy; 2020? 1 degree fov 1 uas 0.6 uas/yr sigma = f(field of view) ADeLA IV, Mexico, Feb. 12,

4 Why the atmosphere is kind of a bummer Light Atmosphere Ground ADeLA IV, Mexico, Feb. 12,

5 The WIYN Observatory University of Wisconsin Indiana University Yale University National Optical Astron. Obs. ADeLA IV, Mexico, Feb. 12,

6 1º (square) field-of-view imager for WIYN Focal plane to sample good seeing images: 0.1 pixel scale Use active tip/tilt correction (up to 20Hz) to improve seeing (by 0.15 in R). Focal plane array of 8x8 thinned Orthogonal Transfer Array CCD chips 1 Gigapixel camera WIYN One-Degree Imager (ODI) Use active tip/tilt correction (up Fast readout time (about 5 sec) for high efficiency F/6.3 beam allows use of narrow band filters Now under construction with a projected first light at the end of cost about $8M USD. Prototype QUOTA (8k x 8k) now in operation. ADeLA IV, Mexico, Feb. 12,

7 Tip-Tilt Corrections Tip-Tilt systems correct for atmospheric motions correct for telescope guiding errors telescope vibrations dominated at right ADeLA IV, Mexico, Feb. 12,

8 Tip-Tilt Corrections A: The improvement in the delivered image quality is about 0.15 for the WIYN median seeing of 0.70 in the R-band. (A) B: Tip-Tilt correction degrades as you move from the guide star. The 50% point is about 4 from the guide star. (B) ADeLA IV, Mexico, Feb. 12,

9 The Ring Nebula and Tip-Tilt ADeLA IV, Mexico, Feb. 12,

10 Tip/Tilt effect on image quality Guide-stars monitored with up to 30 Hz on a subset of the Orthogonal Transfer CCDs Some image motion is correlated over the 1 degree field of view, e.g., due to telescope wind shake and this is easily removed by a global shift Some image motion is correlated over only a 4 arc- minute field of view, also known as the iso-kinetic patch. This is image motion due to atmospheric turbulence and is removed through the use of local tip-tilt charge shuffling on the Orthogonal Transfer Arrays. ADeLA IV, Mexico, Feb. 12,

11 Astrometric precision estimates Positional precision in I-band = ±2 mas/exp (Vieira, et al 2005) Z-band = ±1 mas/exp (projection) igma x ~ ± 0.41 mas (mean of 26 exposures) igma p ~ ± 0.54 mas/yr igma pi ~ ± 0.66 mas Or, a factor of 2 better, if you believe the ± 1 mas estimate for Z ±1 mas positional precision in Z-band/image at S/N~50, or at V ~22.5 for a 4-minute exposure. 60-minute limiting exposure at S/N=10 gives mag = 26 in nearly all bands ADeLA IV, Mexico, Feb. 12,

12 Large-area, deep photometric surveys Carried out on small aperture telescopes for extragalactic studies, but very useful for astrometry: 2MASS (1.3 m), SDSS (2.5 m), INT-WFS (2.5 m). 2MASS (Cutri et al. 2003): Sgr, Monoceros, Canis Major, Tri-And ADeLA IV, Mexico, Feb. 12,

13 Milky Way s Appearance in the Sky Sgr ADeLA IV, Mexico, Feb. 12,

14 Finding Merger Remnants Velocity dispersion in a remnant stream predicted v ~ ± 5 km/s (Helmi & White, 1999; Kathryn Johnston, 2006) remnant streams predicted by H&W within the local 1 kpc 3 D (limit) ~ 1.9 kpc (D = v /*ig ), with ig = 0.54 mas/yr Volume ~ kpc 3 Number of streams in ODI Yale Survey Detection/non-detection of streams could place limits on the validity of the lambda CDM lambdacdm models of cosmology ADeLA IV, Mexico, Feb. 12,

15 The Stellar Census and Dark Matter Parallax precision adopt igma = ±0.66 mas (might be 2x smaller) 10igma pi yields D 150 pc Adopt stars/pc stars predicted in Yale Survey» ± stars/pc 3 Brown dwarfs, L & T dwarfs Detect t to M I 21 at 150 pc Courtesy of Todd Henry ADeLA IV, Mexico, Feb. 12,

16 Open Cluster Membership Survey proper motion precision igma pm ~ ± 0.54 mas/yr Exactly what is needed for precision membership determinations. ti igma pm ~ ± 2.6 1kpc Very clean separation of members from field stars for clusters with D < 1-2 kpc Will start project with QUOTA in 2009 for the central cores of many Open clusters Courtesy of Todd Henry ADeLA IV, Mexico, Feb. 12,

17 Binary stars. Gravitation --> orbit. Traditionally very hard to get good masses. Need SIZE of orbit, which means we need the parallax. Gaia and SIM will do the job here. Orbits and masses. θ θ θ ρ ρ ρ ρ N ρ ρ ρ ρ ρρ ADeLA IV, Mexico, Feb. 12,

18 Binary Star Images t=0.00s t=0.05s t=0.10s t=0.15s ADeLA IV, Mexico, Feb. 12,

19 A smaller separation t=0.00s t=0.05s t=0.10s t=0.15s ADeLA IV, Mexico, Feb. 12,

20 Astrometric Precision at WIYN (Two minute observations) ADeLA IV, Mexico, Feb. 12,

21 VLTI, Keck I, FGS, CHARA, NPOI, etc. can do more (PC simulation) (FGS simulation) Separation = 70 mas It is possible to measure separations down to mas with FGS. ADeLA IV, Mexico, Feb. 12,

22 The Future in Binary Star Research Can determine the orbit, total magnitude, magnitude difference, parallax, and spectrum. From these, derive masses, luminosities, effective temperatures, common metallicity (seven params). That s more than sufficient to constrain standard stellar models (M 1, M 2, Y, Z). Age information, at least in some cases. Chemical evolution (dy/dz)! Indirect information about star formation, environment through statistics. ADeLA IV, Mexico, Feb. 12,

23 Adaptive Optics Adaptive optics can correct for atmospheric turbulence Very useful in the Infrared Very small areas of the sky, say 1 Need a fairly bright reference star to monitor the atmosphere, so limited unless laser reference is used ADeLA IV, Mexico, Feb. 12,

24 The Milky Way s Black Hole Adaptive optics in the Infrared Can see through the 20 magnitudes of visual extinction Measure the mass of the compact object at the Galactic center from orbital motions of the stars ADeLA IV, Mexico, Feb. 12,

25 Space Satellite accuracy projections Mission Position Parallax Proper motion Gaia V < 15 V = 20 6 uas 205 uas 21 uas 275 uas 11 uas 145 uas/yr SIM V < 20 3 uas 4 uas 2.5 uas/yr OBSS 7 < V < 14 V = uas 100 uas 10 uas 100 uas 10 uas/yr 100 uas/yr ADeLA IV, Mexico, Feb. 12,

26 Catalog accuracy with time Dramatic increases in the technology available for astrometry has yielded an unprecedented accuracy increases Space astrometry Hipparcos > ±1 mas HST/FGS > ± 0.2 mas Gaia & OBSS > ± 21 uas SIM > ± 4uas Ground-based astrometry NOFS > ± 0.5 mas ODI > ± 0.2 mas o HST/FGS & ODI OBSS & o SIM -10,000 Apologies to VERA, VLTI, Keck I, NPOI and CHARA! ADeLA IV, Mexico, Feb. 12,

27 Accuracy Intercomparisons s with magnitude Parallax accuracies HIP > ± 1 mas to 8th mag HST > ± 0.2 mas bright stars to 15th mag ODI > ±0.2 mas faint stars 16th to 22nd mag and lower precision to 26th mag Gaia & OBSS ±20 uas to 14th mag decreasing to ±0.1 mas at 20th mag SIM ±4 uas to 20th mag HST/FGS_/ & OBSS / /ODI ADeLA IV, Mexico, Feb. 12,

28 Range of Astrometric Satellites Gaia - Scanning mode Repeated scan visits to achieve faint magnitudes and build accuracy SIM - pointed mode Integrates to achieve faint magnitudes and build accuracy ~10 4 stars OBSS - pointed mode Integrate on field to achieve faint magnitudes and build accuracy QSOs for proper motion and parallax zero points ADeLA IV, Mexico, Feb. 12,

29 Science opportunities Extra-solar planets Galactic cannibalism and cosmology Dark matter and the rotation ti of the Galaxy Orbits of globular clusters, Magellanic Clouds and dwarf galaxies Measure the shape of the galactic spheroid Galactic and extragalactic distance scales Stellar census in the solar neighborhood ADeLA IV, Mexico, Feb. 12,

30 Finding Extrasolar Planets Radial velocity surveys have discovered about 200 extra-solar planets Photometric transit surveys like Kepler will find many more SIM and Gaia will discover and determine extra-solar planet masses using Astrometry ADeLA IV, Mexico, Feb. 12,

31 Kinematics: The Future Distances SIM (18 mag) 1% 10% SIM 2.5 kpc 25 kpc GAIA 0.4 kpc 4 kpc OBSS (14 Hipparcos 0.01 kpc 0.1 kpc mag) Proper Motions: SIM ~ 2.5 uas/yr GAIA ~ 11 uas/yr Hipparcos ~ 1 mas/yr GAIA (15 mag) ADeLA IV, Mexico, Feb. 12,

32 Sagittarius Dwarf Galaxy ADeLA IV, Mexico, Feb. 12, G. Gilmore and R. Sword

33 Galactic cannibalism and cosmology Lambda CDM cosmology predicts many mergers Few are seen, Sag for sure, maybe others Hundreds predicted Interaction strips and destroys merging galaxy in several orbits sigma(vel) ~ 5km/sec in tails Best seen in outer halo Dispersed in inner halo by precession caused by our non-spherical halo Measure debris orbits to determine shape of spheroid ADeLA IV, Mexico, Feb. 12,

34 Perturbed Spiral Galaxies, Tidal Streams M31; Zucker et al NGC 60 NGC 5719 SDSS ADeLA IV, Mexico, Feb. 12, M 104 D. Malin -AAT

35 Understanding the Kinematical Structure of the Milky Way and its Formation 1) Use Galactic satellites, tidal streams, globular clusters as test particles to probe the Galactic potential, and model Galactic interactions. 2) Characterize the main Galactic components disk, thick disk, halo, bulge/bar. i.e., measure their mean velocities, velocity dispersions and the corresponding gradients over the relevant size of each component. Combine the kinematics with chemical information to constrain formation models ADeLA IV, Mexico, Feb. 12,

36 Rotation curves and dark matter Virtually all external galaxies have flat rotation curves Large amounts of dark matter is implied or a Keplerian fall-off would occur The Milky Way s rotation curve is poorly determined It will be trivial to make the MW s curve like 3198 with SIM and Gaia ADeLA IV, Mexico, Feb. 12,

37 Local Group members Beyond the merging satellite galaxies Note that all of the proper p motions are predicted to be large in the context of SIM and Gaia a accuracies 3D velocities of the LG members will provide mass estimates of the LG and dark matter ADeLA IV, Mexico, Feb. 12,

38 The distance to the Galactic Center Baade s & Plaut s windows are low absorption holes towards the Gal. Cen. All space missions will yield 10 sigma parallaxes for a single star!! We now have only 0.2 sigma parallax of the GC from all determinations! The distance scale of the galaxy will be definitively known. ADeLA IV, Mexico, Feb. 12,

39 Cepheids and RR Lyrae stars The extragalactic distance scale Cepheid variables Current M v vs log Period is based on the Mag. Clouds, whose metallicity is different from that of the Milky Way Direct parallaxes of the galactic Cepheids will eliminate the Magellanic Clouds as an intermediate step in the extragalactic distance scale RR Lyrae variables Galactic globular clusters Parallaxes of bright stars in the GCs with different metallicities iti give definitive iti M v s of the RRL s as a function of metallicity, period and age.» Isochrone fitting of the GC s yields the age and metallicity ADeLA IV, Mexico, Feb. 12,

40 Pop II stars Galactic globular clusters Parallaxes of bright stars in the GCs with different ages and metallicities gives: M v = f{[fe/h], age}. Subdwarfs Parallaxes of binary stars gives: M v = f{[fe/h], Mass} ADeLA IV, Mexico, Feb. 12,

41 The Challenges Hipparcos and HST accuracy increase were projected at 10x Very difficult to achieve, but exceeded by the dedicated di d work of teams of astrometrists. t t Gaia, SIM and OBSS projected accuracy increase is a factor of 100x! We will need outstanding astrometrists now and in the near future to achieve/approach that goal. ADeLA IV, Mexico, Feb. 12,

42 Summary The potential for Astrometry to contribute to science is greater than at any time in history! A desperate need exists to train young scientists in Astrometry to make the most of this exciting future. There is a trend, especially in the US, for diminishing support for Astrometry. We need to convince universities, observatories and astronomical institutes to support the education of Astrometrists (and to hire them!!) ADeLA IV, Mexico, Feb. 12,

43 ADeLA IV, Mexico, Feb. 12,