arXiv:astro-ph/0006088v1 6 Jun 2000 ..Kiss L.L. variations amplitude Systematic II. variables semiregular in Multiperiodicity ih aito snta titycci si iasas The the stars. Mira and in mag as cyclic 2.5 strictly as exceed not not is (GCVS), variation does light Stars Variable amplitude of visual Catalogue their General the defini- in the tion to of According (AGB) diagram. branch giant Hertzsprung-Russell asymptotic the pulsat- the are on SRb variables and red SRa ing type of (SRVs) stars Semiregular Introduction 1. 1 2 e words: Key ei- oscillation. suggest radial+non-radial (1.03–1.10) or stars overtone The these high-order too. in ther CVn, found V ratios in phe- period This unambiguously pulsation. beat- detected of a is modes as nomenon separated explained closely is two Leo of RY ing and UMa as- RX outlined observed of the is behaviour while UMa oscillation, nonradial RY in- sig- low-order rotationally in suming with a modulation and of stars amplitude model UMa three duced geometric RX simple report A Leo, UMa). we (RY RY Cyg) modulations amplitude W nificant and Cyg (AF to due halving chaos. weak period of a presence be of the could explanation behaviour alternative first observed An the the in modes. pulsation overtone a third suggest low-amplitude and ratios biperiodic their and the curve and of light pulsation be periods between to coupling The interpreted strong convection. is for hint magnitude possible of compared a order are similar convection time and their The change and ones. sudden earlier the to of data scales current adding col- after and re-analysed lecting been has decrease amplitude gradual conventional the analysis. with wavelet studied and Fourier- are switching) mode and modulations, change frequency and/or physi- (amplitude by the state out cal of changes carried Fundamental estimates astronomers. amateur magnitude visual long-term on years) based (70–90 variables semiregular bright of sample Abstract. edopitrqet to requests offprint Send 00.51 08.16.4) 20(08.15.1, are: codes thesaurus later) Your hand by inserted be (will no. manuscript A&A eateto xeietlPyisadAtooia Obser Astronomical and Physics Experimental of Department mrcnAscaino aibeSa bevr AVO,2 (AAVSO), Observers Star Variable of Association American eietoeape frpttv oechanges mode repetitive of examples two Beside a showing Per Y Mira carbon the of curve light The 1 .Szatm´ary K. , epeetadtie ihcreaayi o a for analysis lightcurve detailed a present We tr:plain–sas AGB stars: – pulsation stars: [email protected] : 1 y Szab´o Gy. , 1 n ..Mattei J.A. and , aoy AEUiest,See,Do ´r9,H62 Hunga D´om H-6720 t´er Szeged, 9., University, JATE vatory, ic tet abig A23-25USA MA02138-1205 Cambridge Street, Birch 5 riso eieua aibe ftpsSaadSbbased SRb and SRa types of variables semiregular of erties (1998), Parkes & (1999). Percy sug- al. been e.g. et has studies, Kiss which empirical modes, overtone by high-order 4th) gested and of 3rd existence to possible (up the Their 1999). and support Gautschy calculations also nonlocal pul- (see “Mira” of region the instability theory sational outlined statistical and convection thermodynamic a time-dependent and using dynamic by the couplings treating suffer survey performed may (1998) linear al. et pulsation, Xiong incompleteness. and serious the from oversimplifying convection or between ignoring Wood 1986), coupling & Cox Fox & (e.g. Ostlie surveys 1982, stability linear earlier stel- cores, the lar around envelopes drawn convective red was extended these 1998, have Since conclusion giants mechanism. al. firm physical et responsible no the however, Bedding about 1999), 1996, al. Desjardins et et & Kiss (Cadmus Percy stars evolution. 1991, several stellar al. in reported and physical were pulsation the Mode-changes the of governing understanding modulations) processes incomplete frequency indicate or different may amplitude of off long-term and modes, on turning overtone repetitive (e.g. of mode-switching, parameters case na- these (in of their changes orders Fundamental and modes, pulsation). non-radial) excited or of periods (radial number follows: ture the as are amplitudes, pulsation and the characterizing eters atmo- extended and the giants. pulsation in red to motions of large-scale spheres due to likely due most partly are for periodicities that curves confirmed main which light variables, measurements semiregular simulteneous bright velocity with several radial comparison presented their Lebzel- (2000) and and al. (1999) simultaneously et Lebzelter Paper many ter pulsation. – of 1999 of al. existence modes et the excited Kiss suggests 1998, al. which et I), (Mattei stars occurs some increasing multiperiodicity is that an evidence been empirical has of be- amount sim- There as relatively environment. a interpreted pulsating in variations ple usually cycle-to-cycle been by their caused has of ing which complexity the curves, to light refers “semiregular” attribute 2 h rtpr fti eisadesdtegnrlprop- general the addressed series this of part first The param- main the view, of point observational the From ASTROPHYSICS ASTRONOMY AND ry 2 Kiss et al.: Systematic amplitude variations in semiregular variables
Table 1. The list of programme stars. Variability types are taken from the GCVS, while periods are those of obtained in Paper I.
GCVS IRAS Type Dataset(s) Periods [JD+2400000] [days] RS Aur – SRa 28485 – 50890 (AFOEV, VSOLJ) 173, 168 V CVn 13172+4547 SRa 37600 – 51208 (AAVSO) 194, 186 23808 – 50907 (AFOEV, VSOLJ, HAA/VSS) W Cyg 21341+4508 SRa 17404 – 50902 (AFOEV, VSOLJ, HAA/VSS) 240, 130 AF Cyg 19287+4602 SRb 22456 – 50902 (AFOEV, VSOLJ, HAA/VSS) 921, 163, 93 RY Leo 10015+1413 SRb 28598 – 50933 (AFOEV, VSOLJ, HAA/VSS) 160, 145 Y Per 03242+4400 M 37602 – 51210 (AAVSO) 245, 127 23057 – 51547 (AFOEV, VSOLJ, HAA/VSS) RX UMa 09100+6728 SRb 17689 – 50808 (AFOEV, VSOLJ, HAA/VSS) 201, 189, 98 RY UMa 12180+6135 SRB 37600 – 51208 (AAVSO) 305, 287
on a set of semiregulars containing almost 100 stars. A few programme stars and details on the datasets are presented special cases were reported to illustrate such phenomena in Table 1. as long-term amplitude modulations, amplitude decrease and mode switching. In the meantime, new and newly computerized archive data were added to those analysed 3. Results on the individual variables previously; therefore, some of the special cases in Paper I 3.1. Changing the type of variability: Y Persei are worth studying in more details. The main aim of this paper is to discuss the observed changes of the pulsational Y Per is a well-known carbon Mira star, though its period properties through well-observed light curves in terms of (about 250 days) is the shortest one among them (Groe- multimode pulsation, possible non-radial modes, coupling newegen et al. 1998). There was no indication of peculiar- between oscillation and/or rotation and convection. Also, ity until 1987, when its amplitude dropped significantly. we want to extend the list of stars with such phenomena Furthermore, it fits exactly the PL relation of galactic car- and to point out that the discussed behaviours are much bon LPVs (Bergeat et al. 1998), thus this star has been more common in red semiregulars than was thought ear- considered as a typical member of its type. lier. The paper is organised as follows. Sect. 2 deals with However, as has been pointed out in Paper I, the ap- the observations and basic data handling, Sect. 3 contains pearance of the visual light curve changed dramatically the results on the individual variables, while a brief sum- around JD 2447000 (1987). The earlier Mira-type vari- mary is given in Sect. 4. ations disappeared and were replaced by a semiregular and low-amplitude brightness change. In order to trace the time-dependent variations and quantify the sudden 2. Observations change, we performed a detailed lightcurve analysis utiliz- ing subsets of the whole dataset. The presented results are based on long-term visual obser- The finally merged and averaged light curve covers vations for eight stars carried out by amateur astronomers. 28500 days (more than 110 cycles). There are smaller gaps The data were extracted from the same international in the fist half of the data, while the second half is com- databases as in Paper I (Association Francaise des Obser- pletely continuous. We divided the data into eight 3000 vateurs d’Etoiles Variables – AFOEV, Variable Star Ob- day-long segments (each containing about 12 cycles) and servers’ League of Japan – VSOLJ, American Association one 4500 day-long segment. This enabled an accurate pe- of Variable Star Observers – AAVSO, Hungarian Astro- riod determination in every segment avoiding the possible nomical Association/Variable Star Section – HAA/VSS). period smearing due to its long-term variation. The period In the meantime newly computerized historic and very re- was calculated with the conventional Fourier-analysis and cent data, collected by the AAVSO1 and VSNET2, have was checked independently with a non-linear regression been added to the earlier observations. The data were analysis. analysed with the conventional Fourier and wavelet anal- Data in the first eight segments can be described very ysis after calculating 5-day or 10-day bins of visual light well with only one harmonic, but the last one with a two- curves depending on the length of the most characteristic component harmonic sum. None of the residuals shows period (see details and references in Paper I). The list of significant periodic signals. The fitted curves are plotted in Fig. 1, while the resulting parameters are presented in 1 http://www.aavso.org Table 2. Although the formal standard errors are quite 2 http://www.kusastro.kyoto-u.ac.jp/vsnet small, the real uncertainties are a little larger, most prob- Kiss et al.: Systematic amplitude variations in semiregular variables 3