Good science with small telescopes

1. 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

2. General considerations • 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.

3. How many hours I can have ? • 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 thanthose 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” ? ).

4. Some examples • 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 • MWC 314 (Serra La Nave) Frasca et al. 2016, A&A, 585, 60 • V381 Lac (Loiano, Asiago, Campo Imperatore) Rossi et al. 2016, MNRAS, 256, 2550

5. GR290 in M33 • 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;

6. The light curve of GR 290 covering more than a century.

7. Spectral evolution of GR290 in 12 years typical W-R star shot phase cold phase

8. Spectral changes in GR 290 as a function of magnitude.

9. GR290 results and model • 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.

10. MWC 314 • 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.

11. MWC 314 Figure 1: radial velocity curve: a) photospheric absorption lines b) blue/redpeak 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

12. MWC 314 variability phase dependence: Radial velocity of the Absorption lines ( S II ) emission lines blue/red peak He I5876lineprofile

13. MWC 314 - model Mass center

14. MWC 314 - conclusions • 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 .

15. 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.

16. 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

17. 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.

18. V381 Lac - SED The SED of V381 Lac Model fit of literature and our own data at different levels of optical-NIR luminosity.

19. V381 Lac - results • 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 havereproduced 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)

20. Final remarks Common features of the researches shown are • Very long time baseline • Dense monitoring • Multiband approach requiring different instrument / telescopes • 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.