SONG – Stellar Observations Network Group

J. Christensen-Dalsgaard1, F. Grundahl1, U. G. Jørgensen2, H. Kjeldsen1,T. Arentoft1, S. Frandsen1 and P. Kjærgaard2

1) Danish AsteroSeismology Centre, University of Aarhus2) Niels Bohr Institute, Copenhagen University

Torben Arentoft talk: Procyon campaign

• Overlapping data from 3 observatories:

Torben Arentoft talk: Procyon campaign

SONG GoalsDo for stars what GONG does for the Sun

well, almost...... (BiSON, IRIS)

- Asteroseismology (Doppler; also daytime solar observations)

Main focus on solar-like oscillators

- Exoplanets (microlensing, Doppler)

Microlensing can potentially detect very small planets Set limits on occurrence of planets

Use Lucky-Imaging (photometry)

SONG asteroseismology – overview

Seismology targets: solar-like stars with V < 6

Long, continuous periods Bright, nearby targets, hence well-

characterized; can get R from interferometry

Relatively few but well studied targets Complementary to the space missions

Doppler velocity – the optimal tool for solar-like asteroseismology

Solar-type star at V=10,

4 years with Kepler

Solar-type star at V=2,

2 × 4 months with SONG

l = 3 can be detected

How will these goals be reached?

SONG baseline configuration:

8 network nodes (4S / 4N) at already existing sites

1.0m telescopes at each node Instruments: spectrograph + lucky imager Optimized for main science goals Automatic operations

The first step is the construction of a full prototype node

Strawman sites Izaña: proposed for prototype

Telescope Aperture: 1m Focal-length: 36m Coudé focus 10” rms. pointing precision No instruments in dome Telescope pier next to instrument container

Focal plane Atmospheric dispersion correction (lucky-

imaging) Field de-rotation Tip/tilt correction (spectroscopy) Calibration light for spectrograph (ThAr, FF) Iodine cell temperature controlled Auxiliary port for other instrumentation

Focal plane layout for SONG (not to exact scale)

Spectrograph slit

Tip-

tilt m

irror

AUX. port

Spectrograph: Characteristics and capabilities

R = 100 000, 1.”3 × 10” slit, 2.5pixel sampling, R4 echelle, 75mm x 300mm Throughput: 55% (slit to CCD camera) Possibility to change slits (resolution). Wavelength range: 4800 – 6800Å with gaps, no Hα or Li on detector. BUT... Good order separation (7-25 pixels), very small line tilt. 2048 × 2048 pixel detector, back. illuminated. Andor. Readout rate: 3MHz @ 12e read-out noise, 5MHz @ 30e RON) Low level of stray-light Iodine cell for velocity reference Very good image quality (80% encircled energy : ø = 5-7µm over detector). Temperature controlled Compact design ( 50 × 90cm)

Spectrograph design and analysis: Paolo Spanò, INAF, Brera

Velocity precision of SONG spectrograph

55s. exposure

Stellar spectrum without iodine

Stellar spectrum with Iodine

Data reduction for an iodine cell

SONG employs an iodine cell as velocity reference.

We have started the development of the SONG iodine cell software

Code is based on IDL – publicly available when developed. Basic version is working.

Flat-fielding and extraction of spectra using REDUCE (Piskunov & Valenti, 2002).

Strategy:

Develop and test software on existing (RAW) UVES data from previous asteroseismology observing campaigns which allows a comparison of results. The adopted procedure is close to that described in papers by Butler and Marcy.

The SONG spectrograph is very similar in layout, resolution and sampling to UVES.

The results presented here represent the first attempt of this on the data obtained byButler et al. (2004).

Enlarge this section

(d)

Zoom of previous figure – agreement with Butler et al. (2004)

is excellent. Grundahl errors are approximately 25% larger.

(d)

from previous figure

76cm/s

Amplitude and power spectra for αCen A,

688 UVES spectra, high-pass filtered.

76 cm/s

70 cm/s

4 months of SONG

observations

Example: sharp features in stellar models

HeII ionization

No overshoot

With overshoot

Oscillatory signals

Houdek & Gough (2007; MNRAS 375, 861)

Fit

He IIBCZ

He I

Simulated SONG data

Full-disk helioseismology with SONG

BiSON

HARPS

Kjeldsen et al. (2008; ApJ 682, 1370)

Beyond asteroseismology Stellar activity Planet search with Doppler velocity Planet search with microlensing

10 days

GOLF

Constraining inclination:

corresponding to the rotation period or half the period (Clarke 2003)

With the known radiusand vsin(i) = 3.16 km s-1

we find:

or

days 5.03.10 SlowP

o

o

i

i

739

318

(Ulrich et al. 2000)(Garcia et al. 2005)

Torben Arentoft talk: Procyon campaign

Velocity background

From GOLF data

Velocity detection of planets

Microlensing observations Follow up of high-amplification events discovered by OGLE or

MOA (and LSST etc.) Only a small field of view needed (46" × 46") Planetary events have durations less than 24h Continuous coverage for entire duration of event is desirable Microlensing has already produced several planet discoveries

as well as limits on the occurrence of planetary systems. However, more events with better coverage are desirable

and the fields are very crowded - good image quality is a big advantage

FOV 2' x 2'

The field of the recent 5.5 Earth mass Planet discovered by microlensing.

Beaulieu et al. (2006; Nature 439, 437)

Lucky-Imaging

Camera f.o.v: ~46" x 46", 0."09 pixels, from Andor.

only for 4500Å and longwards 2-colors simultaneous (split @ 700nm). filter mechanism possibly simultaneous 2 color photometry +

spectroscopy provide signal for tip/tilt correction

Planned schedule

2006 – 2007: Conceptual design 2008: Prototype Phase A 2009 – 2011: Prototype design, construction

and test 2012 – 2014: Network construction 2014 – ????: Network operation

Current status of SONG

Funding situation Major funding from:

Villum Kann-Rasmussen Fondet (Velux)

Danish Natural Sciences Research Council

This is sufficient for the full prototype phase

Prototype schedule

Funding situation

Prototype schedule- 2008: finish optical design/layout, ordering

- 2009: mechanical design, building of instruments

- 2010: assembly, integration, test (instr, tel)

- 2011: assembly (Tenerife) – live test on sky.

Current status of SONG

SUMMARY

SONG is singing ! High-resolution spectrograph (4800-6800), accurate velocities

Dual-colour imaging with high duty-cycle (small field) Dual-colour imaging AND spectroscopy (probably)

First light for telescope: late 2010 On-site testing 2011

Workshop in Aarhus, Last half of March, 2009

http://astro.phys.au.dk/SONG