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SPECTROSCOPY
One Concept for 3 Instruments
A comparison of 3 Echelle spectrographs with a similar design but different aims:
UV-Visual Echelle Spectrograph (UVES) at the VLT (8m.) (‘99)
Fiber Extended Range Optical Spectrograph (FEROS) at ESO 1.52m (‘98)
High Accuracy Radial velocity Planet Searcher (HARPS) at ESO 3.6m (‘03)
L. Pasquini July 2002
SPECTROSCOPY
UVES Science Objectives
•Structure, physical conditions and abundances of interstellar and intergalactic gas
at early epochs from absorption spectra of high redshift QSO’s
•Kinematics of stars and gas in galactic nuclei
•Kinematics and mass distribution of stars clusters
•Composition, kinematics and physical conditions of the interstellar medium in the
•Galaxy and in nearby systems
•Chemical composition and atmospheric models of galactic and extragalactic stars
•Substellar companions of nearby stars (high precision RV over long time-scales)
•Stellar oscillations
!
DEFINITELY A GENERAL PURPOSE FACILITY!
L. Pasquini July 2002
SPECTROSCOPY
FEROS Science Objectives
• Accurate RV surveys (not planet search)
• Chemical composition of stars
• Line profiles of different types and their variability (Stellar Activity,
Doppler imagining, Pulsations)
•
•
•
Search for Diffuse Interstellar Bands (DIBS)
Highly Variable Objects (e.g Novae, SNe)
Regular Monitoring of objects
General Purpose, but focalized … emphasis on the time
availability of small telescope
L. Pasquini July 2002
SPECTROSCOPY
HARPS Science Objectives
•Detection of Extra Solar Planets
• Radial Velocity Survey with long term
accuracy of 1 m/sec
DEDICATED INSTRUMENT !
L. Pasquini July 2002
SPECTROSCOPY
UVES Tec. Specs (abridged)
•Working Wavelength range: 300-1100 nm. Whole range with less than 6 exposures
•Maximum Optical Efficiency over the whole Range, > 20%
•Limiting magnitudes: S/N = 10 in 2 Hours U=18.7, V=19.4 with slit losses 30%.
•Spatially Resolved spectroscopy, Derotator, Guiding, pre-slit optical quality
•Sampling: better than 4 pixels/arcsecond
•R as function of slit width 1” -> 41000; 0.25”--->107000
•Order Separation: Minimum 15 arcseconds, slight height continuously variable
•Stray Light: source stray less than 5% , ghost less than 10**-3, diffuse light < 1
e/pix/h
•Velocity stability: better than 150 m/sec/hour
•Parallel Blue and Red observations
L. Pasquini July 2002
SPECTROSCOPY
FEROS Tech. Specs (abridged)
•Fibre fed spectrograph, Permanently mounted, capability of switching with B&Ch
in
5 minutes
•Large Spectral Coverage (370-860 nm), without gaps in one frame
•Large Throughput (18%@370, 27%@400nm,40% @ larger wavelengths )
•Two fibres: second for SKY or Simultaneous Calibration (or polarimetry..)
• RV accuracy: 50 Meters / sec long term
• Resolving Power: > 25.000
• ADDITIONAL
• No Movable parts (minimal maintenance)
• Thermally stable environment, automatic compensation of Camera Focus ..
• Data Reduction Software, On-Line pipeline
L. Pasquini July 2002
SPECTROSCOPY
HARPS Technical Specs (abridged)
•
Use of the Simultaneous Th-A Calibration Technique (Geneve, Corelie,
Elodie) (developed after CORAVEL, Mayor & Queloz 1995, Queloz et al.
1998)
• R> 80.000 (e.g. with pixel=1 km/sec 1m/sec=1/1000 of 1 pixel!)
• Coverage: 380-680 nm.
• Mechanical Stability, vacuum
• Efficiency: V=9 star S/N ratio = 100 in 2.5 minutes,
• Operations: minimise overheads
• Suitable calibration AND procedures to establish short and long term
accuracy
•
Data Reduction and operations is PART of the instrument, to produce
Radial Velocities as PRODUCT for the user.
L. Pasquini July 2002
SPECTROSCOPY
Radial Velocity accuracy: some aspects
σ(RV) ~ (S/N)^-1 * Range^(-0.5) * R^(-1) (Hatzes and Cochran 1992 )
Resolving Power, Signal to noise and Spectral range (more correct probably is
Q factor, Bouchy et al. 2001).
If Systematic effects are relevant, higher Resolving power becomes more important..
Two Main Techniques used:
Self Calibrating Cell (Iodine Cell) : + same optical path, Many lines
- Loss of light, Limited Spectral Range,
Complex DRS.
Simultaneous Calibration (Geneve): + Very Efficient, Simple DRS
- Not same light path; where are the limits ?
L. Pasquini July 2002
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
Doppler-shifted spectral lines
+v
-v
m*sin(i)
Period
Distance
Eccentricity
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
Why do we need HARPS ?
s=10 ms-1
RV of Jupiter
s=1 ms-1
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
Why do we need HARPS ?
s=10 ms-1
s=1 ms-1
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
Why do we need HARPS ?
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
Object spectrum
ThAr spectrum
Wavelength calibration
0
RV
Object
fiber
ThAr
reference
RV
0
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
Object spectrum
ThAr spectrum
Measurement
RV (object) =
RV (measured)
0
- RV(drift)
RV (measured)
RV
Object
fiber
ThAr
reference
RV(drift)
RV
0
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
Simultaneous ThAr reference
Iodine absorption cell
• Attained long-term accuracy: 2-3 m/s
• Attained long-term accuracy : 2-3 m/s
• Spectral range: 380 - 690 nm
• Spectral range: 500 -600 nm
• Efficiency: 100%
• Efficiency: 50%
• Entire spectral information available
• Not suitable for spectroscopy
Simultaneous ThAr is 5 times more efficient than Iodine cell !
Ex.: HARPS on 3.6m telescope is equivalent to UVES on VLT
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
G8V star
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
Halo stars
G dwarfs
K dwarfs
M dwarfs
Tint = 15 Minutes
Volume limited
sample 50 pc
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
Radial Velocities
Microarcsecond Astrometry
• Does not provide sini
• Provides sini
• Provides m2sini, a, P, e
• Provides m2, a, P, e
• Sensitive to short periods
• Sensitive to long periods
• Accuracy does not depend on distance
to the star
• Accuracy does depend on distance to the
star
• Accuracy does not depend on spectral
type
 f(m2,sini,a,P,e,Fe/H)
• HARPS (sim. Reference)
• PRIMA (available soon, long-term)
• UVES (iodine cell, Flames)
• SIM, GAIA (2009 +)
• FEROS
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
Stellar oscillations, Bouchy & Carrier 2001
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
Transits:

COROT

KEPLER

EDDINGTON
Thousands of short-period planets
detected and P determined
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
Transit on HD 209458
HST
Brown et al., 2001
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
Transits:

COROT

KEPLER

EDDINGTON
Thousands of short-period planets
detected and P determined
However: NO MASS!
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
The only way to get the mass …
… by RV measurements!
mp[M]
K 0.09
m/s
a[AU]M[M]
σK  σRV
Nobs/2
Example:
5 M around M0 star at 0.1 AU

K = 2.0 m/s
with sRV = 1 m/s and Nobs = 50

mass accuracy 10%
 Mass and mean density
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
SPECTROSCOPY
Light Injection (pre-spectro)
FEROS: 2.7” Aperture, MICROLENSES, FIBRES, IMAGE SLICER
(2*resolution), PROJECTOR
UVES: Variable aperture (0.2-5”), Variable Height SLIT(S), De-ROTATOR,
Atmospheric Dispersion Compensator, FILTERS, DICHROIC, Blue and Red Slits,
Iodine Cell, Image Slicer … …
HARPS: ADC, MICROLENSES, FIBRES, IMAGE SCRAMBLER
L. Pasquini July 2002
SPECTROSCOPY
The basic Design
White Pupil Spectrograph
Two Collimators (double pass!)
COATINGS!!
Echelle
Folding Mirror
Crossdisperser
Camera
L. Pasquini July 2002
COATINGS!!
SPECTROSCOPY
The basic Design
White Pupil Spectrograph
Two Collimators (double pass!)
COATINGS!!
Echelle
Folding Mirror
Crossdisperser
Camera
L. Pasquini July 2002
COATINGS!!
SPECTROSCOPY
Otical Train
White Pupil (Baranne 1988): Exit Pupil as Entrance Pupil is set at the entrance of
the Camera ; big advantage is the small camera, no vignetting.
L. Pasquini July 2002
SPECTROSCOPY
UVES Optomechanics
Double arm (Red-Blue)to
optimize efficiency,
simultaneous observations
with dichroic, image slicer
for (R=10^5), iodine cell
in pre-slit.
26 movable functions!
Within the Red arm the 2
Detectors are optimized
L. Pasquini July 2002
SPECTROSCOPY
UVES optomechanics
UVES opened in the
integration hall in
Garching: the RED camera
and the RED X-disperser
are mounted.
Note also the crowded pre
slit area.
L. Pasquini July 2002
SPECTROSCOPY
FEROS Optomechanics
The single larger optical components in FEROS were the X-disperser prims
and the main collimator
L. Pasquini July 2002
Calibrations:
• Spectral flatfield
• ThAr spectral lamp
• Iodine absorption cell
3.6-m ESO telescope + HCFA
Two-fiber mode
Reference fiber
Object fiber
Mono mode
Astrophysical niches of high-resolution spectroscopy
Image Scrambler
ES0 Santiago, 2-3 Oct. 2001
SPECTROSCOPY
HARPS optomechanics
L. Pasquini July 2002
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
Astrophysical niches of high-resolution spectroscopy
ES0 Santiago, 2-3 Oct. 2001
SPECTROSCOPY
Summary of Characteristics
UVES
FEROS
Pupil (cm)
20
13.5
Echelle
41.6,31.6 R4
79 R2
R*A
40000
70000
Xdisp
Gratings(4)
Prism
Camera
F/1.8,2.5
F/3
CCD (15 mm/pix) 3*2X4K
2X4K
Arcs/Pix
0.22/0.16
.65
(Km/Pix)
1.6,1.2
3.0
Min.Order Sep.
10”,15”
30Pix
Aperture
variable (>0.2) 2.7”
Coverage (nm) 285 or 485
560
L. Pasquini July 2002
HARPS
20.8
31.6 R4
90000
Grism
F/5
2*2X4K
0.19
0.7
34 Pix
1.”
300
SPECTROSCOPY
Summary of Characteristics
Should note a few points:
The use of a large (79 lines/mm) groove numbers allows to FEROS:
a) To have a prism as X-disperser and still have a decent minimum
separation: larger free spectral range
b) On the other hand this would not allow higher resolution: with
smaller slit higher magnificaion, less Km/sec/pix ---> No longer
order coverage, CCD too small!
c) HARPS can allow better sampling than UVES because
1) Spectral range limited at 690 nm in the red
2) Low S/N ratio observations are not the main driver!
L. Pasquini July 2002
Understanding K Giants
results from radial velocity measurement
Johny Setiawan, 04 June 2002
People
Johny Setiawan (KIS)
Oskar von der Lühe (KIS)
Luca Pasquini (ESO)
Artie Hatzes (TLS, Tautenburg)
Licio da Silva (ON, Brazil)
Leo Girardi (Univ. Padova)
QUESTION
Do all giants show RV variations ? As suggested by the handful sofar sudied?
What is causing these variations ? Pulsations? Activity-induced modulation?
Planets ?
85 stars have been observed Oct 99 - Feb 02
77 stars have been analyzed for RV
Variability ?
Black: current targets
Red : proposed new targets
Fibre-fed Extended Range Optical
Spectrograph
Wavelength coverage
Resolution
CCD
RV accuracy
3700-8600 Å
39 orders, 2 fibres
48000
2098 x 4096 pixel
50 m/s (contract)
23 m/s (comissioning)
26 m/s (end of mission)
Calibration modes:
object - sky
object - simult. calibration
Results (1): The spectrograph accuracy
Accuracy of standard star:
HD 10700, G8V, mV =3.50
26 m/s (moderate, but still enough for K giants)
Feb 01-Oct 01
Results (2): Trend along the RGB
60-100 m/s
40-60 m/s
26-40 m/s
Binaries not included in the figure
Results (3): binary system
Detected:
12 stars with stellar companions (binaries / multiple systems)
Not yet in catalog
m2 sin i ~ 0.33 MSun
at 2.4 AU
m2 sin i ~ 0.21 MSun
at 1.0 AU
Results (4): short, long, multi-periodic variation
Observed: 46 stars show RV variations due to pulsations and/or rotation
Short period
(several days)
multi-periodic
Scargle periodogram:
LP ~ 450 d
SP ~ 14 d
Results (5): comparing stellar parameters
Computed: stellar radius, rotational velocity V sin i, rotation period
Results (6): stellar activities
HD 50778: RV variation long period, estimated radius ~ 19.8 RSun
D
A
B
C
Activity index = (A+B)/(C+D), Choi et al. 1995
Results (6): stellar activities
HD 7672, active binary, estimated period < 50 days, orbit ~ 0.28 AU
Results (7): brown dwarfs
Detected:
possible brown dwarfs companions around HD 27697, HD 156111
m2 sin i ~ 106 MJup
at 1.40 AU
m2 sin i ~ 91 MJup
at 1.16 AU
Results (8): planets (?)
Detected:
possible planetary companions around HD 47536, HD 110014 (?)
P / sin i (370 days) < Pmeasured (>600 days)
no correlation : activity index vs. RV variation
Results (8): planets (?)
Aug 2001
High metallicity [Fe/H] = +0.06 (Buzzoni, et al. 2001)
Photometry : HIPPARCOS least variable star , s = 0.0007 mag
(Adelman S.J, 2001)
P/ sin i (380 days) < Pmeasured (550 days)
Activity index correlated to RV variation ?
Results (9): the rest (11 / 77)
etc ...
No significant RV trend, unsufficient data,
big observation gap, ...
Summary :
There is a trend in the RV variation along the RGB,
which is in a good agreement with the photometric survey
(Henry et al. 2000)
Typical RV variation of G and K giants is rms = 60 m/s
Typical P / sin i is 100-300 days for giants R < 20 RSun
this may explain the past observations of K giants
(Smith 1988, Larson 1993, Hatzes et al.)
Posibilities of companions can be detected with the RV
method if K1 > 60 m/s and P > 300 days