1. Polaris: Return to Bygone Pulsational Activity?
Igor Usenko, Valery Kovtyukh Astronomical Observatory, Odessa National University,
Odessa, Ukraine
Anatoly Miroshnichenko, Stephen Danford
Dept. of Physics & Astronomy,
University of North Carolina at Greensboro

2. Cepheid Instability Strip (CIS)

3. Why is Polaris Interesting?
α UMi = Polaris is a unique object for astrophysical research due to the following:
It is the nearest yellow supergiant and Cepheid
Distance:
d = 107 pc R = 39.3 Rʘ “P-L-relation” (Arellano Ferro, 1984).
d = 119 pc R = 42 Rʘ “P-L-relation” (Fernie et al., 1995).
d= 99 ±4 pc R = 33± 2 Rʘ “AF dwarfs from open cluster” (Turner 2005)
d = pc R = 37.6 Rʘ “Polaris B distance” (Usenko & Klochkova, 2007)
d = ±9.0 pc R = 46± 3 Rʘ (HIPPARCOS)
d = 132±8 pc R = 46± 3 Rʘ “Stellar interferometry” (Nordgren et al., 2000).

4. Why is Polaris Interesting?
Chemical composition (from spectra):
Observed Predicted (3rd CIS crossing)
[C/H] = 0.17± 0.18
[N/H] =
[O/H] = 0.00± 0.02
[Fe/H] = +0.07±0.10
M = M (Usenko et al. 2005)

5. Why is Polaris Interesting?
Polaris is a multiple system with three visual components (Polaris B = BD+88º9, C, and D).
Polaris is a member of an anonymous open cluster.
Polaris is one of four Cepheids with a radius measured by optical interferometry (463 R, Nordgren et al. 1999).
Polaris has the largest number of radial velocity measurements over ~120 years among Cepheids.

6. Why is Polaris Interesting?
Pulsation period was found gradually increasing by 4.450.03 sec a year from to days in 18962004 (Turner 2005).
Pulsation amplitude decreased from ~5 km/s before 1950 to ~0.05 km/s in the 1980’s.
Pulsation amplitude began increasing again in from ~1.5 km/s in 1987 to ~2.4 km/s in 2007.

7. Why is Polaris Interesting?
Polaris itself (Polaris A) is a specroscopic binary: yellow supergiant Aa ( F8 Ib) and companion Ab (A-F V) with orbital period 29.9 yr (Dinshaw et al. 1989).
Besides the both pulsational and orbital periods there are 45- and 119- days periods else, concerned with Aa rotation, existence of cool or macroturbulent velocity spots, or otherwise non-radial pulsations.

8. Polaris observations: difficulties and benefits
Its proximity to the North celestical pole is needed a special telescope mount.
Its magnitude (<V> = 2.0) and luck of suitable reference stars of comparable brightness in its immediate vicinty for photometrical observations.

9. Polaris observations: difficulties and benefits
Its brightness allows to use the small telescopes equipped by spectrographs with
R~10000 and more to obtain the radial velocity and effective temperature estimations from spectra with σ of ±1 km/s and ±15 – 20 K, respectively.

10. Polaris pulsational amplitude decreasing

11. Polaris pulsational amplitude decreasing

12. Effective temperature and color-index: secular variations
Symbols: crosses - Stebbins (1946); open circle - Williams (1966); triangles - Fernie (1966); open stars - Feltz & McNamara (1980); diamond - Henden (1980); open squares - Arellano Ferro (1983); filled circles - Fernie et al. (1993); filled square - Brown & Bochonko (1994); stars - Usenko et al. (2008).

13. Pulsational RV amplitude lacuna 1997 -2003

14. To fill this lacuna we have used old spectroscopic observations (56 spectra) from:
1m telescope, Ritter Observatory, Univ. of Toledo, Ohio, USA, fiber-fed echelle spectrograph (R~26000);
2.1m Otto Struve telescope, McDonald Observatory, Texas, USA, SANDIFORD spectrograph (R~48000);
6 m BTA telescope SAO RAS (Russia); spectrographs LYNX (R~25000), PFES (R~17000), NES (R~50000)

15. Recent Radial Velocity Variations
RO – Ritter Observatory (U. Toledo, Ohio)
SAO – Special Astrophysical Observatory (Russia)

16. Last RV observational monitorings 2004-2007 (Lee et al. 2008)

17. New Polaris RV observational project

18. Three College Observatory (TCO)
Location: Alamance County, 8 mi S of Graham
Telescope: 0.81-m Cassegrain, F/13.6
Equipment: Apogee CCD with BVRH filters
Eshelle-spectrograph, Shelyak Instr., France with an SBIG ST7 ( ) and ATIK (2013) CCD

19. TCO Telescope

20. The Spectrograph
Fibers (F/5): 50-m object and a 200-m calibration

21. CCD Cameras for Spectroscopy
ST7-XMEI
765x510 pixels
9-m size
ATIK-460EX
2200x1400 pixels
4.5-m size

22. Goals Observations Determine atmospheric parameters
Monitor radial velocity variations and pulsation period
Observations
Eshelle spectrograph at the 0.81m telescope of the Three College Observatory
Spectral range 42507800 Å
24 spectral orders
Signal-to-noise ratio in continuum over 100
25 spectra were taken in SeptemberDecember 2015
Each spectrum consists of 6  30 individual spectra, each 2060 sec exposure time

23. Polaris Spectrum Example
Part (~40%) of an echelle spectral order, taken on 2015/10/23
Signal-to-noise ratio in continuum ~300

24. TCO Spectra: Results and Analysis
Radial Velocity phase curve
Effective Temp. phase curve
Teff mean accuracy: 15 – 20 K

25. TCO Spectra: Results and Analysis

26. Results:
Pulsation period: days – 13 minutes longer than in 2007
Radial Velocity amplitude: 4.2 km/s – twice larger than in 2007
Evolutionary conclusion: Polaris moves toward the CIS red edge
RV amplitude changes carried both sporadical and secular character

27. Probable reasons: Stellar evolution and pulsational activity
Multiplicity
Envelope presence

28. Polaris within the Cepheid Instability Strip (Usenko et al. 2005)

29. Orbital periods of Polaris A (Usenko et al. 2007)

30. RV estimates of Polaris during six-point stars- metal lines, five-point stars - Hα, open circles - Hβ

31. Hα line core profiles during 2003-2004

32. New observations
More 20 spectra have been obtained during last two months.
The observations do go on !

33. What we will plan ahead:
To continue these observations next years
To obtain the spectra as much as possible
To look for collaborators
It is quite enough to obtain 1-2 spectrograms per night using small telescopes.

34. THANK YOU !