J/MNRAS/448/464 JHK lightcurves of red giants in the SMC (Takayama+, 2015)
Using broad-band photometry to examine the nature of long secondary periods
in red giants.
Takayama M., Wood P.R., Ita Y.
<Mon. Not. R. Astron. Soc., 448, 464-483 (2015)>
=2015MNRAS.448..464T 2015MNRAS.448..464T (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; Stars, giant ; Photometry, VRI ;
Photometry, infrared ; Effective temperatures ; Spectral types
Keywords: circumstellar matter - infrared: stars
Abstract:
Long-term JHK light curves have recently become available for large
numbers of the more luminous stars in the Small Magellanic Cloud
(SMC). We have used these JHK light curves, along with OGLE (Optical
Gravitational Lensing Experiment) V and I light curves, to examine the
variability of a sample of luminous red giants in the SMC which show
prominent long secondary periods (LSPs). The origin of the LSPs is
currently unknown. In oxygen-rich stars, we found that while most
broad-band colours (e.g. V- I) get redder when an oxygen-rich star
dims during its LSP cycle, the J-K colour barely changes and sometimes
becomes bluer. We interpret the J-K colour changes as being due to
increasing water vapour absorption during declining light caused by
the development of a layer of dense cool gas above the photosphere.
This result and previous observations which indicate the development
of a chromosphere between minimum to maximum light suggest that the
LSP phenomenon is associated with the ejection of matter from the
stellar photosphere near the beginning of light decline. We explore
the possibility that broad-band light variations from the optical to
the near-infrared regions can be explained by either dust absorption
by ejected matter or large spots on a rotating stellar surface.
However, neither model is capable of explaining the observed light
variations in a variety of colour-magnitude diagrams. We conclude that
some other mechanism is responsible for the light variations
associated with LSPs in red giants.
Description:
This is JHK light curves of 7 oxygen rich stars and 14 carbon stars
which show the variability of prominent long secondary periods (LSPs).
Those stars are cross-identified with OGLE LSP variables in the Small
Magellanic Cloud (Soszynski et al. 2011, J/AcA/61/217).
A long-term multiband near-IR photometric survey for variable stars in
the Large and Small Magellanic Clouds has been carried out at the
South African Astronomical Observatory at Sutherland (Ita et al., in
preparation). The SIRIUS camera attached to the IRSF 1.4 m telescope
was used for this survey and more than 10 yr of observations in the
near-IR bands J(1.25 µm), H(1.63 µm) and KS(2.14 µm) band were
obtained. In this work, we select the SMC stars from the SIRIUS data
base. We obtained the V- and I-band time series of SMC red giants from
the OGLE project (Soszynski et al. 2011, J/AcA/61/217).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 90 21 Basic parameters of the program stars at
maximum light
phot/* 57 123 Individual J, H and K band time-series of stars
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See also:
II/288 : IRSF Magellanic Clouds Point Source Catalog (Kato+ 2007)
J/A+A/401/873 : The SMC in the Far Infrared (Wilke+, 2003)
J/AcA/61/217 : VI light curves of SMC long-period variables (Soszynski+, 2011)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- Name Name (OGLE SMC-LPV-NNNNN in Simbad)
20- 28 F9.6 deg RAdeg Right Ascension in decimal degrees (J2000)
30- 38 F9.5 deg DEdeg Declination in decimal degrees (J2000)
40- 44 F5.2 mag Vmag ? OGLE V-band magnitude
46- 50 F5.2 mag Imag OGLE I-band magnitude
52- 56 F5.2 mag Jmag IRSF J-band magnitude
58- 62 F5.2 mag Hmag IRSF H-band magnitude
64- 68 F5.2 mag Ksmag IRSF KS-band magnitude
70- 73 I4 Lsun L Luminosity derived by applying a bolometric
correction to Ks (see Section 4.1)
75- 78 I4 K TBB Blackbody temperature derived from J-KS
80- 83 I4 K Teff Effective temperature derived from J-KS using
the formula in Bessell, Wood & Evans
(1983MNRAS.202...59B 1983MNRAS.202...59B)
85- 88 I4 d PLSP Prominent long secondary period (LSP)
90 A1 --- SpType [OC] Spectral type (Oxygen or Carbon-rich)
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Byte-by-byte Description of file: phot/*
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Bytes Format Units Label Explanations
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1- 14 F14.6 d JD Julian date
16- 21 F6.3 mag mag 2MASS J-, H- or K-band magnitude
23- 28 F6.3 mag Errana Error in deferential image analysis
31- 35 F5.3 mag Errmag Error in reference magnitude
38- 42 F5.3 mag Erroff Error in conversion offset
44- 55 A12 --- Reg Name of the survey region in which the variable
star is detected (SMCNNNN-NNNN)
57 A1 --- Subreg [ABCDEFGH] Name of the survey subregion in which
the variable star is detected (1)
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Note (1): For more details, see Ita et al., in prep.
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 14-Nov-2017