First considerations on possible

preliminary and complementary

programmes for the SIAMOIS project

Ennio Poretti INAF – Osservatorio Astronomico di Brera

To observe a known Delta Sct or Gamma Dor star from South Pole.

The study of these stars by a single instrument operating in a continuous way is a very good starting point and a new observationalfacility.

Hopefully, we can remove of the spurious peaks usually populating the low frequency region (f<5 c/d) of the power spectra of spectroscopic and photometric timeseries.

g-modes, which should be present in both types of stars, should beautifullystand up in the power spectra.

Among Delta Sct stars, there are only three candidates

Rho Pup F0 Dec -24 V=2.83 v sin i = 15 km/s 51 Sgr A1m -24 5.64 13 Rho Pav A9V -32 4.86 45

Thy are others stars listed in the SIAMOIS webpage (AI Vel, V703 Sco,RS Gru, SX Phe) satisfying the requirements Dec < -30 and v sin i > 40 Km/s,but they are High Amplitude Delta Sct stars (evolved stars, most radial pulsators)

Among Gamma Dor stars, there are three candidates

Gamma Dor F4III Dec -51 V=4.20 v sini i = 50 km/s HR 2740 F0IV -46 4.50 51 HD 147787 F4IV -64 5.27 spectroscopic binary

Not an exciting scenario …

What we have as observational background ?

Gamma Dor (itself!) V=4.20, v sin i=50 km/s Balona et al. 1996 ESO, MSSSO, NZ, SAAO

Frequencies 1.32, 1.36, 1.47 c/dAmplitudes around 1-2 km/s

HR 2740

Gamma Dor variable V=4.5, v sin i=51 km/s Poretti et al. 1997 , SAAO+ESO campaign

Bunch of frequencies very close to 1.0 c/d.

The frequency content of Gamma Dor variables is an hard task also for multisite campaigns.

SIAMOIS spectral window will be more effectivein this context.

Rho Puppis Delta Sct variable V=2.81, v sin i = 15 km/s Dall & Frandsen 2002 1.54 Danish telescope at La Silla DFOSC in echelle mode, R=4300

Line indices of Balmer lines,proportional to EW, thussensitive to temperaturevariations.

Monoperiodic, radial pulsator.

Mathias et al. (1997) suggestthe presence of nonradial modes.

51 Sgr = HD 184552 Delta Sct variable

4 hours of photometry in 1991 at ESO 50 cm Hildebrandt 1992

Noted in SIMBAD as a spectroscopic binary

Searching for new ones ?

A few numbers …

When considering subgiant and dwarfs with Dec < - 20 we get

25 stars with V < +2 52 stars with 2<V<3 138 stars with 3<V<4 404 stars with 4<V<5 1271 stars with 5<V<6

1890 stars in total

Let’s consider subgiant and dwarfs V<6.0 stars with Dec < -30

435 stars Spect. Type < A0 , 217 with a vsini value285 A0< Spect. Type < F5 , 132 603 Spect. Type > F5 , 19

1323 stars in total, 368 only with an available vsini value …

Extensive search for photometric variability:

- photometric facilities (bright stars) used for COROT are in the North (OSN, SPM, Mercator, …) - availability of photometric telescopes in Australia, New Zealand, South Africa ? - too few targets per nights, a lot of nights

Search for spectroscopic characterization:

- availability of medium class telescopes (SAAO, ESO,…) but OPCs maybe hard to convince.

Preliminary consideration :

Too many stars for limited resources

Put severe constraints on the targets, to choose ina well defined and limited sample (not an easy task anyway…)

Example of a severe constraint:

to limit the search in a restricted area of the HR diagram

Example of restricted area :

The cold border of the instabilitystrip, where Gamma Dor andDelta Sct are both present, and

maybe hybrid pulsator too.

Complementary programme(when SIAMOIS will be operating)

Difficult to identify the surviving observational facilitiesafter 2008:

- photometric follow up of bright stars could be problematic;

- spectroscopic follow up for mode identification with very high S/N spectra will be still feasible, with new instruments too;

- extension of the velocity radial measurements during South Pole “day” from Southern Hemisphere (SAAO, ESO, ….)