1 tauvex and agns t tauvex=tel a aviv university uv ex uv explorer
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TAUVEX and AGNs
TAUVEX=TTelAAviv UniversityUVUV ExExplorer
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Outline
• Background• Technical description• Projected performance• Scientific projects (AGNs)• Conclusions
3IUE: all targets
Why UV?
Earth atmosphereopaque to UV
Low sky background!
UV range
Background
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Short history of UV astronomy
• UV range definition: 10 nm to 380 nm• First observation: Sun, from V2 (US-NRL)• First satellite: TD-1. Sky survey to ~9
mag
• First spectroscopy: Copernicus• Longest duration: IUE• Most expensive: HST (only part is UV)
TD-1 starlight at 156.5 nmin 3° bins (Sujatha et al. 2004)
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Generic UV Targets
• Comets• Hot stars (high-
mass, evolved [WD])
• Galaxies: evolution• Interstellar & Inter-
Galactic matter• AGNs
SMC
Hyakutake
Hale-Bopp 40 deg
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TAUVEX history
1989: chosen as 1st priority by ISA1991: agreement to launch with SRG1994: planned launch date2000: delays with SRG; start search for alternate launch2003: ISA-ISRO agreement2007: planned launch on GSAT-4
SRG=Spectrum Roentgen-Gamma(incarnation I)Prime contractor: El-Op,
Electro-optical Industries
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• GSAT-4 to geo-synchronous orbit.• Platform=technological demonstrator for new generation of Indian communication satellites.• TAUVEX has a dedicated communication channel of 1 Mbps, continuously.• Satellite has fixed orientation w.r.t. the Earth!
• To allow unrestrictedaccess to the sky, TAUVEXis mounted on orientableplatform (MDP).
The Indian connection
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Toward Earth
MDP in launch orientation. MDPmotion is up to 180º from the launch position, to -90≤δ≤+90
δ=0º
δ=+90º
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•3x20cm RC telescopes•~One-degree images•Angular resolution ~7”•UV “solar blind” sensitivity•Unblocked area ~266 cm²(3x)•On GSAT-4, sky scans
TAUVEX basicsTechnical description
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TAUVEX: filter setup
Each telescope with 4-position wheelOne position blocked (shutter=CLS)Three positions with filters
Filter arrangementT1: SF1SF1, SF2, BBF, CLST2: SF2, SF3SF3, BBF, CLST3: SF1SF1, NBF3, SF3SF3, CLS
Includes geometric shadowing, 2 mirrors, lenses+windows, filter trasmission & detector QE
CaF_2cutoff
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Simulated image
Drift rate:“Pixel”=3 arcsecMax. “no-smear” time=1/8 sec
Basic timescale for data frame
Object in FOV: 224 sec along detector diameter at δ=0 (basic exposure time)
High declination advantage!(above 81º, more than 1500 sec per pass)
sec/cos15 ''
TAUVEX performance(and constrains)
Projected performance
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Confusing magnitudes…
21.01(NUV) 22.8
ticmonochroma 19.70(FUV) 22.6limit 1 MIS
19.01(NUV) 20.8
ticmonochroma 17.10(FUV) 20.0limit 1 AIS
Angstromcms erg][
40.2log5log5.2
:
175.21log5.2
:atic)(monochrom
1-2-1-
f
fAB
GALEX
fm
TAUVEX
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TAUVEX vs. HST
•144x more collecting area than TAUVEX•70-700x better resolution•400x smaller FOV (STIS)•200-400x higher cost
Only operating UV instruments at present are ACS & WFPC-2!
HST has:
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GALEX
•GALEX launched April 2003 for all-sky UV survey•GALEX (1x) and TAUVEX (3x) have similar collecting
areas and angular resolution•GALEX has one 50-cm telescope and only two spectral
bands: FUV & NUV•GALEX operates only 1/3 of the orbit
AIS like TAUVEX singlepass (AB mag limit=18 mono)
GALEX NUV=TAUVEX BBF
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TAUVEX - performance
• Exposure depth depends on:– Dwell time of object in FOV (“exposure”)– Level of background (Max count rate~100K/sec)
• Background is stray light: light scattered into the detectors from sources external to the FOV
• Strongest source=SunSun
• Operational solutions:– Filter choice (solar spectrum)– Sky strip selection– Baffle extension
•Scattered into baffle•Reflected by solar panels & thrusters
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Sensitivity (best case) SF-1
SF-2
SF-3
BBF-worstcase
BBF-bestcase
To Sun
Equal-area projection of celestial hemisphere
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GALEX vs. TAUVEX• GALEX: DIS=80 sq.
degrees (~70 fields).
• Limiting AB=25 (1σ); only small part done yet
• TAUVEX: DEC=+90 to +85 is equivalent area to DIS
• Limiting mag’s (5σ) for single scan are:– SF1-3: 18-20
monochromatic (AB=21-23)
– BBF: gain one mag
To surpass GALEX DIS, TAUVEX requires 10 scans of the Polar Cap area! This is 1-2 months of observations.
GALEX DIS field: Groth region,14ksec exposure
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TAUVEX science: AGNs
• Detection (star-AGN photometric separation)
• Rough redshift determination (UV dropouts)
• Variability studies
Composite AGN spectrum (Telfer et al. 2002, ApJ 565, 773)
Projected results
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How many low-z AGNs?
LIMMAG
20.0019.5019.0018.5018.0017.5017.0016.5016.00.
30
20
10
0
BB
SF1
SF3
AGNs per square degree, with z<1, to different limiting magnitudes.
Conclusion:
TAUVEX will find significant numbers of low-z AGNs
N
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Red≡stars, green≡galaxies, light blue≡AGNs.+reddening GALEX+SDSS (Bianchi et al 2004)
GALEX AGNs: UV vs. optical colors
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Colors vs. redshift
-1.5
-1
-0.5
0
0.5
1
1 2 3 4 5 6 7 8 9 10
10*z
Colo
r (m
ag)
SF1-SF2
SF2-SF3
U-B
B-V
V-R
TAUVEX: UV+optical colors
Color-color plot
-0.5
-0.4
-0.3
-0.2
-0.1
0
-1-0.500.5
SF1-SF2
SF2
-SF
3z
Nearby AGNs (z<1)
UV-UV
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UV-Optical
-0.1
0
0.1
0.2
0.3
0.4
0.5
-1-0.500.5
SF1-SF2
V-R
z
UV-Optical
0
0.2
0.4
0.6
0.8
-0.6-0.4-0.20
SF2-SF3
B-V
z
TAUVEX: UV+optical colors
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Color-color
-0.6
-0.4
-0.2
0
0.2
0.4
-2-101
SF1-SF2
SF2
-SF
3
z
[email protected]<z<4, including Ly limit and Ly forest
Importance of simultaneous UV & optical measurements!Importance of simultaneous UV & optical measurements!
AGN colors
-2
-1
0
1
2
3
1 2 3 4 5 6 7 8
z/0.5
Colo
r
SF1-SF2
SF2-SF3
U-B
B-V
V-R
UV-UV
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Conclusions
TAUVEX offers similar performance to GALEX, with important enhancements:– Three simultaneous bands– Five different filters (flexibility)– Time-resolved photometry over a
number of time scales: 1/8 sec to 100s of sec for single pass; revisits
Launch 20 February 2007
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TAUVEX on GSAT4: GENERAL VIEW
New features:•Rotating plate•Front radiator•Extra baffle•Extra shielding•Thermal couplings
MDP
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Performance: SF-1
Equal-area plot, hemisphere
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Performance: SF-2
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Performance: SF-3
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Performance: BBF
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TAUVEX: detection system
Wedge (A)Strip (B)
Zig-zag )C(
Detection=(x, y, t)
window
CaF2
(Approx. 700“pixels” acrossFOV)
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TD-1A & IUE
All-sky photometric surveyto 9 mag
Targeted mission: spectroscopy
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TAUVEX science: stars & ISM
B star UV spectrum
Use SF2 and NBF3to measure the EWof the ISM band
TD-1PAHs distribution?
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TAUVEX science: galaxies
UV light understandphysics of star-forming processes, extinction
Late-type galaxies=good targets
GALEX 1300 sec image
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Antennae galaxies (NGC4039/4039):importance of the UV sensitivity to establish the nature of stellar populations and determine the full IMF
TAUVEX science: galaxies II
HαLyman cont`.
FUV, NUVHot stars (O,B,A)
Optical (UBVRI)Stars (F,G,K,M)
Near-IRStars (K, M)
Almoznino & Brosch 1998
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TAUVEX science: galaxies III
UV observations track the history of star formation in the last billion years
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TAUVEX science:UV-dropouts (cosmology)
Select z=1-2 galaxiesfrom UV dropouts
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Real image: distortion pattern“Flat-field” (collimator)
TAUVEX: lab performanceNext
More? More?
Edgedischarge
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SURVEYArea [deg]
Length [Month]
Expos [ksec]
m limlog #Gals
Volume<z>Comments
All-sky (AIS)40,00040.120.5710.1Galactic caps first
Medium Imaging (MIS)100021.5236.5~10.6SDSS, 2dF overlap
Deep Imaging (DIS)804302571.00.85Fields
Ultra-Deep Image (UDIS)10.2200265.50.050.9Fields
Nearby Galaxy (NGS) 3000.50.527.5 m per sq. deg.
2.5------Galaxy List
Wide Spectroscopic (WSS) 80430204.50.030.15Same fields as DIS
Medium Spectroscopic (MSS)
8230021-234.50.040.5Centers of WSS
Deep Spectroscopic (DSS)24200022.5-244.50.050.9Fields
Guest Investigator Cycle 1---4---------------
GALEX surveys
(AB)
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GALEX-technical
•Uses dichroic beamsplitter•Two crossed-delay line MCP detectors (2kx2k)•Insertable grism for low-resolution spectra•Pegasus launch to LEO
Pegasus launch
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• Assume best case=no stray light
• Performance (S/N=5) with SF-2 for stars of different spectral types
• Lines for monochromatic mag. 17, 18, 19, 20, 21 star
OO
BB AA GG
(better than GALEX!)
TAUVEX: performance (GSAT-4)