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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.

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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 observational


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 beautifully

stand up in the power spectra.


What we have as observational background ?

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 …


Gamma Dor (itself!)

V=4.20, v sin i=50 km/s

Balona et al. 1996


Frequencies 1.32, 1.36, 1.47 c/d

Amplitudes 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 effective

in 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, thus

sensitive to temperature


Monoperiodic, radial pulsator.

Mathias et al. (1997) suggest

the 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 value

285 A0< Spect. Type < F5 , 132

603 Spect. Type > F5 , 19

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


Preliminary consideration :

Too many stars for limited resources

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.

Put severe constraints on the targets, to choose in

a well defined and limited sample (not an easy task anyway…)


Example of a severe constraint:

tolimit the search in a restricted

area of the HR diagram

Example of restricted area :

The cold border of the instability

strip, where Gamma Dor and

Delta Sct are both present, and maybe hybrid pulsator too.


Complementary programme

(when SIAMOIS will be operating)

Difficult to identify the surviving observational facilities

after 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, ….)