Pulsating stars plethora of variables and observational tasks

Transcription

1 Pulsating stars plethora of variables and observational tasks László Szabados Konkoly Observatory, Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences Tatranská Lomnica, 24 September 2013

2 Variable stars are astrophysical laboratories. Pulsating stars provide us with information on the internal structure of the stars and stellar evolution (see the H-R diagram). Several types of luminous pulsators are useful distance indicators (P-L relationship).

3 Credit: H. Jeffery Oscillations in stars can be excited in various phases of stellar evolution from pre-main sequence to post-agb stages. Hot and cool stars, dim and luminous stars can also pulsate. Different excitation mechanisms exist.

4 Soszynski et al. (2006) Period-luminosity relationships for several types of pulsating variables. Increasing importance of binarity among pulsating stars.

5 Photometry of pulsating variables is a realm of small telescopes. The temporal coverage (duration of the time series) is critical for studying multiperiodicity, changes in frequency content, modal amplitudes, etc. Such observational project cannot be competitive for large telescopes, in spite of their astrophysical importance.

6 Accuracy of ground-based observations HD (Martinez et al. 2000) HD (Joshi et al., 2000) Accuracy of space photometry is up to micromagnitudes (below: a Kepler GDOR variable by Tkachenko et al., 2013)

7 From microvariability to large amplitudes From hours to years in periodicity Eyer & Mowlavi (2008)

8

9 This is only a partial list! Missing types include e.g., anomalous Cepheids, UU Her type variables, hot subdwarf stars, etc.

10 Complications Different types of variability may be present simultaneously in a given star: e.g. pulsating+rotating variables; pulsating+eclipsing variables; pulsating+cataclysmic variables; pulsation+erratic variability in premain sequence stars. From the point of view of astrophysics this is good but it causes problems in analysing and interpreting the observational data. As to pulsating variables, there is no unique classification. GCVS: 33 types (and subtypes) VSX (@AAVSO): 53 types. In the GCVS (47811 variables in July 2013): 8533 RR Lyr; 8098 Mira; 932 classical Cepheids; 762 δ Sct; 414 Type II Cepheids; 209 β Cep; 85 γ Dor; 80 white dwarf pulsators. A smaller number of variables, however, does not mean that the given type of variables is less important Massive photometric surveys: tens of thousand new variables not catalogued in the GCVS.

11 Gamma Doradus type variables (Grigahcéne et al., 2010) ~80 DSCT; several GDOR+DSCT hybrids; SPB in the Kepler field. WASP-33: exoplanet host star with DSCT pulsation; Ppuls: min, Porb: 26 times longer (Herrero et al., 2011).

12 (Balona, 2010) Dozens of excited frequencies asteroseismology internal structure of the stars

13 Pulsating pre-main sequence variables in NGC 6530 (Zwintz & Weiss, 2006)

14 ~40 roap stars are known. noap stars (not oscillating Ap stars) occupy a similar part of the HR diiagram as the roap stars. Interaction of pulsation and magnetic field. Balona (2010) Discovery of DSCT and GDOR pulsation in Ap stars from Kepler data (Balona et al., 2011) HD (Joshi et al., 2000)

15 B type pulsating variables; discovery of a new type (Mowlavi et al., 2013) Light curve of SPB pulsators (Aerts et al. 2010; Gruber et al. 2012)

16 Light curve of the LBV AG Car SPB supergiant HD (Aerts et al., 2010) (Saio et al., 2006; MOST) O type stars: HD periodic mass-loss episodes due to an oscillation mode (Aerts et al., 2010)

17 Variable white dwarfs Type Year of discovery ZZ Cet 1968 GW Vir 1979 V777 Her 1982 V361 Hya 1997 V1093 Her 2002 (Balona, 2010) Light curve gallery of white dwarf variables (Aerts et al., 2009)

18 Light curve gallery of subdwarf variables (Aerts et al., 2010) Extreme He-stars (Jeffery, 2008) Pulsators: PV Tel, BX Cir type; Less than 15 are known in our Galaxy.

19 R CrB also pulsates (Kameswara Rao & Lambert, 1997) Synhronization of the decline events (Crause et al., 2007)

20 AAVSO light curves of T UMi (above): He-shell flash and R Cen (below): Mira SRb period: 550 d 510 d Amplitude: 6.3 mag 2.8 mag Correlation between the pulsation period and semi amplitude of the Mira variable R Cen (Hawkins et al., 2001)

21 RR Tel: Symbiotic Nova, erupted in 1948 (Robinson, 1975) FG Sge (post-agb, CSPN, pulsation, RCB) (Jurcsik & Montesinos, 1999)

22 Heartbeat variables (Kepler discovery): Tidally excited pulsations in eccentric binaries Top: KOI-54 (Welsh et al., 2011) A gallery of stellar heartbeats (Thomson et al., 2012) There is a CoRoT heartbeat candidate, HD (Hareter, 2013)

23 CoRoT EB + DSCT + GDOR (Chapellier & Mathias, 2013)

24 Binary stars among Cepheids are important for the calibration of the P-L relationship. Eclipsing binaries involving a Cepheid component are known in the Magellanic Clouds. In our Galaxy: anomalous Cepheids, TYC (Sipahi et al., 2013), V1135 Her (Khruslov 2008, Sipahi et al., 2013) are members in an eclipsing system. Multicolour photometry binarity can be revealed. Methods are listed by Szabados (2007) and Klagyivik & Szabados (2009). Influence of the companion: photometric, astrometric, physical (luminosity, parallax, pulsation.

25 SZ Lyn (Derekas et al., 2003) DSCT AW Per (Vinkó, 1993) CEP SXPHE CY Aqr (Sterken et al., 2011) SPB HD (Sódor et al., in preparation) Light-time effect in the O-C diagram Listen to the talk by Marek Wolf tomorrow

26 Evolution of classical Cepheids Turner et al. (2006)

27 Different kinds of period changes in the pulsation of Cepheids. Top: RS Pup long-period Cepheid, stellar evolution + erratic fluctuations (Szabados, unpubl.) Bottom: Polaris binarity induced phase jump in the pulsation (Engle & Guinan, 2012) + secular changes in the pulsation amplitude. Unique case?

28 Metallicity from photometry Determination of metallicity ([Fe/H]) from the Fourier decomposition of the light curve of Cepheids (Klagyivik et al., 2013). There is a similar possibility for RR Lyrae type variables (Kovács & Zsoldos, 1995; Jurcsik & Kovács, 1996).

29 V473 Lyr Blazhko effect in a classical Cepheid (Molnár et al., 2013)

30 Beat (double-mode Cepheids): in our Galaxy 40 are known. LMC 90 F/1OT OT/2OT + 2 1OT/3OT SMC 59 F/1OT OT/2OT MW 24 F/1OT OT/2OT M33 5 F/1OT (Moskalik, 2013) In M31: 17 candidates with Pan-STARRS (Lee et al., 2013). Metallicity dependence of the period ratio (Sziládi et al., 2007): Petersen diagram (Marquette et al., 2009)

31 Nonradial modes are excited in 9% of the 1OT Cepheids in the LMC ( f <0.13 c/d). The same phenomenon appears in two F/1OT double-mode Cepheids. Challenge to the pulsation theory. Mysterious period ratio: < P/Pmod < In about 150 Magellanic Cepheids; only in 1OT and F + 1OT pulsators. Parallel sequences in the Petersen diagram (Soszynski et al., 2010)

32 V1154 Cyg: the only Cepheid in the Kepler field. Period jitter in Cepheids pulsating in the first OT. (Derekas et al., 2012)

33 Type II Cepheids in the HRD (Percy, 2007) Subtle light-curve changes in Type II Cepheids IX Cas (Turner et al., 2009) ST Pup (Kiss et al., 2007) Strong changes in the pulsation period of Type II Cepheids BL Her models: period doubling bifurcations en route to chaos (Smolec & Moskalik, 2013)

34 RU Cam, a unique Type II Cepheid (Kolláth & Szeidl, 1993)

35 Later evolutionary phase: RV Tau IW Car (top) RVB AI Sco (middle) RVB TX Oph (bottom) RVA (ASAS light curves; Grzegorz Pojmanski) Relation between binarity and RVB feature (long-period variation in the mean brightness) Post-AGB PPN

36 Blazhko effect: slow, cyclic (not periodic) modulation of the light curve (both amplitude and phase). Observed in both RRab and RRc type variables. Its origin is a century-long enigma. Models: magnetic oblique rotator, cycles in the convection, resonance between a radial mode and nonradial mode. Kolenberg (2006) RR Lyrae stars in Messier 3 (animation by Radek Smolec)

37 Kolenberg (2011) Based on Kepler data new dynamical phenomena have been discovered: period doubling (RR Lyr, Molnár et al. 2012), high-order resonances (RR Lyr, Molnár et al. 2012), three-mode pulsation (V445 Lyr, Guggenberger et al., 2012; RR Lyr, Molnár et al. 2012).

38 Skarka & Cagas (2013) Blazhko effect occurs in about 50% of the field RRab stars. Catalog of Blazhko modulated RR Lyr stars known in the Galactic field : 242 variables including 8 stars with more than one modulation period, and 4 stars with strongly changing modulation period (Skarka, 2013).

39 Double-mode RR Lyrae stars (RRd): < P1/P0 < F + 1OT: 986 in the LMC 258 in the SMC ~170 in the Milky Way field and bulge. F + 2OT 9 known variables in the MW (period ratio is close to 0.59; Moskalik, 2013) Nonradial modes in RR Lyrae stars: 4 RRc stars in the Kepler field with P/Pmod ~ 0.62; Subharmonics of the secondary frequency is excited period doubling AQ Leo: frequencies from the MOST light curve (Gruberbauer et al., 2007)

40 V823 Cas (Jurcsik et al., 2006) Triple-mode pulsator

41 Triple-mode pulsators Table taken from the paper by Wils et al. (2008). GSC is now designated as DO CMi. According to CDS: AC And: V823 Cas: V829 Aql: DO CMi: RR Var. Star EB of Algol type DSCT + 8 triple-mode Cepheids in the Magellanic Clouds: F/1OT/2OT: 3 in the LMC, 1 in the SMC 1OT/2OT/3/OT: 2 in the LMC, 2 in the SMC V823 Cas: strange period changes (Jurcsik et al., 2006)

42 Plethora of optical telescopes Small telescopes overwhelm in the contribution to the cumulative mirror area. In addition to ground-based equipments, photometric space telescopes (most of them have small aperture), and their photometric data are accessible in most cases.

43 Plethora of new variables Gaia (ESA s astrometric space probe) will start in 20 Nov Astrometry and photometry of a billion stars. Expected: 18 million variable stars Estimated number of variable stars to be observed by Gaia (Eyer & Cuypers, 2000): Cepheids (9000 according to Windmark et al., 2011) RR DSCT M SR 3000 BCEP SPB Data of major ground-based sky surveys (Pan-STARRS, LSST) will also offer plenty of new targets with variable brightness (including pulsating variables) for thorough photometry with small or medium aperture telescopes.

44 Variety of observational tasks and their outcome Determination of variability type for newly discovered variable stars; new types are still possible (e.g., brown dwarf pulsation is predicted by theory but unobserved yet) Detailed study of individual variables: - period determination - multiple periodicity, mode identification - discovery of slightly excited non-radial (or radial) modes - separation of different types of variability (pulsational + nonpulsational (e.g., due to rotation, binarity, flares, other episodic phenomena) and many other astrophysically important studies based on photometry of pulsating variables. Determination of physical properties of the stars from the analysis of the light variations: evolutionary state, internal structure, metallicity, rotation, presence of companion(s), etc. Selection of really interesting/important pulsators deserving an indepth (spectroscopic) study with larger telescopes. Cooperation between several telescopes/observatories is beneficial.

45 Recommended recent literature: Aerts, C. Christensen-Dalsgaard, J. Kurtz, D. W. (2010): Asteroseismology, Springer Balona, L. A. (2010): Challenges in Stellar Pulsation, Bentham Science Percy, J. R. (2007): Understanding Variable Stars, Cambridge Univ. Press Suárez, J. C. Garrido, R. Balona, L. A. Christensen-Dalsgaard, J. (eds.) (2013): Stellar Pulsations. Impact of New Instrumentation and New Insights, ASSP 31, Springer Acknowledgments: ESTEC Contract No /12/NL/KML, OTKA K83790 THANK YOU FOR YOUR ATTENTION (Animation by Z. Kolláth)