Transcript prova1 - Chianti Topics

Good science with small telescopes
Corinne Rossi
Università La Sapienza, Roma
Antonio Frasca
INAF/OACT
Roberto Nesci
INAF/IAPS – Roma
Roberto Viotti
INAF/IAPS – Roma
General considerations
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Astronomical research is still “curiosity driven”.
The astronomical objects have apparent luminosities
ranging 10 powers of 10 (i.e. 28 magnitudes excluding
the Sun).
Time scale variabilities range from milliseconds to
centuries.
Therefore it is necessary to use different instruments
depending on the kind of research
It is not a matter to decide if it is better to use big or
small telescopes, but of what kind of research we want
to do, and why.
How many hours I can have ?
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The cost of building and maintenance of a telescope
increases with the cube of its diameter;
The amount of light gathered increases with the square
of its diameter;
Therefore it is not convenient to use a large telescope to
perform a research possible with a smaller one.
It is also clear that large telescopes are necessarily
much fewer than those of smaller size: the observational
time available at a large telescope is therefore much
lower of that available on smaller ones.
Given that the number of astronomers is much larger than
the number of telescopes, it is necessary to evaluate the
different research fields and grant the time to the most
promising ones (or those most “a la page” ? ).
Some examples
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Three examples of astronomical research which
would not be possible if the astronomical community
had only a handful of 8-meter class instruments
available.
GR 290 in M33 (Loiano, Asiago, others)
Polcaro et al. 2016, arXiv 160307284, AJ, in press
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MWC 314 (Serra La Nave)
Frasca et al. 2016, A&A, 585, 60
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V381 Lac (Loiano, Asiago, Campo Imperatore)
Rossi et al. 2016, MNRAS, 256, 2550
GR290 in M33
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Gr290(the Romano star) is a Luminous Blue Variable
(LBV) in the galaxy M33 discovered with the Asiago
Schmidt telescope.
photometric and spectroscopic monitoring from
2003 to 2015 using several telescopes, mainly Cassini
and Copernico, plus photometry from the 37 cm
telescope in Frasso Sabino and the 80 cm in Tenerife.
The data revealed interesting peculiarities, namely:
constant B-V color index despite the large variability
in apparent luminosity;
the spectral type constantly hotter than other LBVs;
The light
curve of
GR 290
covering
more than a
century.
Spectral
evolution
of
GR290 in
12 years
typical
W-R star
cold phase
shot phase
Spectral changes in
GR 290 as a function of
magnitude.
GR290 results and model
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We have found a tight correlation between
spectral type and visual magnitude.
The temporal evolution indicate that the spectrum
is evolving towards a stable WNL phase
characterized by a low visual luminosity.
The spectra were reproduced by CMFGEN
models , which produced the physical parameters of
the present evolutionary phase (wind velocity,
radius, Teff, luminosity, initial mass ).
Important result is that the bolometric luminosity is
variable, being higher during the phases of higher
optical brightness.
MWC 314
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MWC 314 : a single-lined spectroscopic binary system. It
comprises one of the most luminous stars in the Milky Way
and an invisible but massive companion.
The fundamental parameters of the visible spectrum are
similar to those of LBVs, although no large photometric
variations have been recorded.
The purpose of our study was to clarify the origin of the
radial velocity and line profile variations exhibited by
absorption and emission lines.
A dense monitoring from 2007 to 2009 with the
FRESCO spectrograph at the 91cm telescope of the
Catania Observatory; resolving power R=21,000.
In some cases we were able to follow the target for
several consecutive nights.
MWC 314
Figure 1: radial velocity curve:
a) photospheric absorption lines
b) blue/red peak of emission lines
interpreted as superposition of a broad
emission from a region between the two
stars and a static excess absorption
encompassing the circumbinary space.
c) v_hel of permitted emission lines
(continuous line)
d) forbidden emission lines
variability phase
dependence:
Radial velocity of the
Absorption lines
( S II )
emission lines
blue/red peak
He I 5876 line profile
MWC 314
MWC 314 - model
Mass center
MWC 314 - conclusions
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accurate determination of the orbital elements ( P, k ,
e ) and the mass function f(m) from the radial velocity
curve of the absorption lines .
Possible model of the geometry of the system from
velocity and profiles of metallic emission lines
Correlation between stellar wind variability and orbital
phase from the profile of He lines changing from a nearly
symmetric emission to P-Cygni profile.
Detection of extended circumbinary region from the
nitrogen forbidden lines, not affected by the orbital motion :
constant velocity (fig1-d) and line profile .
V381 Lac
V381 Lac was known to be an irregular variable, that
had shown features typical for carbon type star in a
single low resolution spectrum of the Byurakan survey.
Coordinated photometric and spectroscopic
campaigns between 2012 and 2016 performed with
the Cassini and Copernico telescopes in the optical
and the AZT-24 telescope of Campo Imperatore in the
near infrared.
Observational data: rapid and deep changes in the
spectrum and extreme variability in all bands.
Most notably NaI D lines changed from deep absorption
to emission, and [N II] doublet 6548-6584 A emission
progressively grew, strongly related to the simultaneous
photometric fading.
V381 Lac
Spectra ov V381 Lac
at different luminosities:
13 Sep. 2014 18.17
21 Aug 2014 17.85
17 Dec 2013 15.93
18 Oct 2012 12.33
20 Jun 2015 15.45
06 Sep 2015 18.50
V381- Lac infrared
IR color-color plot
of a sample of
carbon stars.
V381 Lac occupies
the positions
labelled by
numbers at different
epochs.
Photometry by
AZT24 telescope of
Campo Imperatore.
V381 Lac - SED
The SED of V381 Lac
Model fit of literature and
our own data at different
levels of optical-NIR
luminosity.
V381 Lac - results
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The general framework emerging from our monitoring
of V381 Lac is that of a cool AGB carbon star
undergoing episodes of high mass ejection and
severe occultation of the stellar photosphere
reminiscent of those characterising the R CrB stars.
By modeling the physical parameters of central star
and of the circumstellar mass distribution we have
reproduced the SED at different epochs
(The referee (Clayton) asked us to continue to monitor
this star, which is apparently the coolest of the known
R CrB stars)
Final remarks
Common features of the researches shown are
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Very long time baseline
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Dense monitoring
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Multiband approach requiring
different instrument / telescopes
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All these items require the flexible availability of
the telescopes and substantial observing time,
which is possible only with “low cost” (i.e. small)
instruments.