March 22, 2010 Science with the William Herschel Telescope 2010-2022
H-band multi-objectspectroscopy around the Galaxy
Carlos Allende Prieto (IAC)
and the APOGEE Team
March 22, 2010 Science with the William Herschel Telescope 2010-2022
APOGEE
• A high-resolution (R~30,000) high-S/N
H-band spectroscopic survey of 100,000 stars in the Galaxy
• Why high-resolution? Why in the H-band? Why now?
March 22, 2010 Science with the William Herschel Telescope 2010-2022
Rationale
• Red giants/red clump have strong NIR flux. Complete point source sky catalogue to H ~ 13.5 available
from 2MASS• AH / AV = 0.17 (x 100 in flux at AV ~6) • Access to dust-obscured galaxy • Velocities to <1 km/s accuracy and precision abundances (15 elements) for giants across the Galaxy• Low atmospheric extinction makes bulge declinations
accessible from North (though over smaller field)• Avoids thermal background problems of even longer
March 22, 2010 Science with the William Herschel Telescope 2010-2022
APOGEE Science Case
• In the context of Galaxy structure and evolution: sampling the distribution functions (x, v, Z) of the Milky Way avoiding the biases of working at visible wavelengths
• In a broader context: does the Milky Way fit in a -CDM universe?
March 22, 2010 Science with the William Herschel Telescope 2010-2022
Terra incognita
• Local thin disk well studied (Geneva-Copenhagen, S4N, Fuhrmann papers …)
• Local and more distant halo well studied (SDSS)
• Local thick-disk well-studied (just recently)• Not the case for the bulge (only Baade’s
window explored) or distant parts of the Galactic disk
March 22, 2010 Science with the William Herschel Telescope 2010-2022
Specific objectives• Disk/Rotation Curve
Surveys of stellar disk dynamics outside solar vicinity typically <~100 starsHI tangent point analyses assume circular rotationinsensitive to non-axisymmetric effects (e.g., arms) andinoperable outside solar circle [V(>Rsun) poorly known]s I
Gradients/lack of gradients in the thin/thick disks o Gas/stars in the spiral arms
• Galactic Bar• Little current data, but possibly wide-ranging influence. Radial
motions affect gas-mixing, metallicity gradients• Bulge
Poorly known. Connection of velocities and chemistry provide s strong constraints on inflow of material into bulgear
• Halo• Internal dynamics of substructure. Inner/outer halo dichotomy
March 22, 2010 Science with the William Herschel Telescope 2010-2022
What makes APOGEE’s spectrograph unique?
• We know: Phoenix (KPNO 2.1m,4.1m, CTIO 4m, Gemini South), NIRSPEC (Keck), CRIRES (VLT)
• We heard of NAHUAL (GTC), CARMENES (3.5m CAHA)
R range detectorPhoenix 50,000-80,000 1-5 m 0.5x1 K
CRIRES <100,000 0.95-5.2 4x0.5x1K
NIRSPEC 25,000 (2,000) 0.95-5.5 1x1 K
March 22, 2010 Science with the William Herschel Telescope 2010-2022
What makes APOGEE’s spectrograph unique?
• Focused in the H band• Larger detectors• Grating (VPH vs. echelle): spectral coverage, efficiency• Multi-object (300 fibers)
APOGEE 30,000 1.5-1.7 3x2x2 K
Phoenix 50,000-80,000 1-5 0.5x1 K
CRIRES <100,000 0.95-5.2 4x0.5x1K
NIRSPEC 25,000 (2,000) 0.95-5.5 1x1 K
March 22, 2010 Science with the William Herschel Telescope 2010-2022
Hardware Overview
Camera
VPHgrating
Fibers in & LN-2 autofill
Collimator
Fold 2 (dichroic)
Fold 1
Detector Assembly (mounts to Camera)
Fiber RacetrackSlithead
(fiber “launch”)
March 22, 2010 Science with the William Herschel Telescope 2010-2022
Hardware overview(Univ. of Virginia)
• Fibers (high-transmission low frd): 40 m H-band optimized (65% throughput). Prototypes near top expectations in hand
• Design includes a dichroic (cutting out thermal IR)
Thanks to Fred Hearty for passing all the info!
March 22, 2010 Science with the William Herschel Telescope 2010-2022
Collimator
March 22, 2010 Science with the William Herschel Telescope 2010-2022
VPH
• Size matters. Design calls for a 50x30 cm grating!
• 3 recorded panels on a single gelatin substrate, sandwiched by two
2.5-cm layers.
Several prototypes have
demonstrated feasibility
(should be done in April)
March 22, 2010 Science with the William Herschel Telescope 2010-2022
Volume Phase Holographic (VPH) Grating
March 22, 2010 Science with the William Herschel Telescope 2010-2022
Camera• All lenses
built and coated
assembly to
begin in two
weeks
• 3 Teledyne
2048x2048
detectors
(same as for JWST)
QE~85% (dithering capabilities!)
March 22, 2010 Science with the William Herschel Telescope 2010-2022
Camera
March 22, 2010 Science with the William Herschel Telescope 2010-2022
Camera
March 22, 2010 Science with the William Herschel Telescope 2010-2022
Cryostat
• All spectrograph cooled to 80 K in vacuum• No entrance window• Cryostat is 2.5x1.5x1.5m• Vibration isolated with common commercial
solutions (>99% removed at >10 Hz)• Active thermal control (~1e-3 K)• Multiple calib. Sources (ThAr, U, laser comb)• Cryostat had 1st vacuum test, ready for 1st cold
test. Delivery should happen in April
March 22, 2010 Science with the William Herschel Telescope 2010-2022
March 22, 2010 Science with the William Herschel Telescope 2010-2022
March 22, 2010 Science with the William Herschel Telescope 2010-2022
March 22, 2010 Science with the William Herschel Telescope 2010-2022
Deliveries• A rich window sampling 15+ Elements (including C,N,O)• R~30,000 provides<<1 km/s velocity errors(probably much much smaller, but stellar jitter)• Fully automated reduction + analysis pipeline• 300 fibers on, 1e5 stars using bright time 3 yrs on ARC 2.5m
March 22, 2010 Science with the William Herschel Telescope 2010-2022
WHT• An APOGEE-like spectrograph on WHT would be
a different instrument: smaller field, different science (e.g. clusters, extra-galactic red giants, integrated extragalactic globular clusters)
• APOGEE, the spectrograph, costs is estimated at ~ 7 M$ (but much cheaper to repeat!)• Concept fully proven• Pipeline/acquis. Software can be recycled• IAC is negotiating full participation in SDSS-III
(i.e. in APOGEE)
March 22, 2010 Science with the William Herschel Telescope 2010-2022
Another interesting example …VIRUS on the HET