J/ApJ/812/12 S-index and Stroemgren LC of HD30495 (Egeland+, 2015)
Sun-like magnetic cycles in the rapidly-rotating young solar analog HD 30495.
Egeland R., Metcalfe T.S., Hall J.C., Henry G.W.
<Astrophys. J., 812, 12 (2015)>
=2015ApJ...812...12E 2015ApJ...812...12E (SIMBAD/NED BibCode)
ADC_Keywords: Photometry, uvby ; Stars, G-type
Keywords: dynamo; stars: activity; stars: individual: HD 30495;
stars: rotation; stars: solar-type
Abstract:
A growing body of evidence suggests that multiple dynamo mechanisms
can drive magnetic variability on different timescales, not only in
the Sun but also in other stars. Many solar activity proxies exhibit a
quasi-biennial (∼2yr) variation, which is superimposed upon the
dominant 11 year cycle. A well-characterized stellar sample suggests
at least two different relationships between rotation period and cycle
period, with some stars exhibiting long and short cycles
simultaneously. Within this sample, the solar cycle periods are
typical of a more rapidly rotating star, implying that the Sun might
be in a transitional state or that it has an unusual evolutionary
history. In this work, we present new and archival observations of
dual magnetic cycles in the young solar analog HD 30495, a ∼1Gyr old
G1.5V star with a rotation period near 11 days. This star falls
squarely on the relationships established by the broader stellar
sample, with short-period variations at ∼1.7yr and a long cycle of
∼12yr. We measure three individual long-period cycles and find
durations ranging from 9.6 to 15.5yr. We find the short-term
variability to be intermittent, but present throughout the majority of
the time series, though its occurrence and amplitude are uncorrelated
with the longer cycle. These essentially solar-like variations occur
in a Sun-like star with more rapid rotation, though surface
differential rotation measurements leave open the possibility of a
solar equivalence.
Description:
We analyze a combined 47-year time series of the Mount Wilson S-index
shown in Figure 1. The combined S time series contains 1285
measurements from five different instruments.
The majority of the measurements (624 measurements from 1967 to 2003)
come from the original Mount Wilson survey, calibrated as described in
Baliunas et al. (1995ApJ...438..269B 1995ApJ...438..269B).
The next largest portion of the measurements are from the
solar-stellar spectrograph (SSS) at Lowell Observatory (364
measurements from 1993 to 2014).
Observations from the SMARTS Southern HK survey using the RC Spec
R∼2500 spectrograph at 1.5m telescope at CTIO are the third largest
contribution (140 measurements from 2008 to 2013).
We add 108 measurements from 2011 to 2015 derived from HARPS R∼120000
spectra.
Finally, we add 49 observations from 2002 to 2008 derived from R∼55000
spectra of the Hamilton Spectrometer at Lick Observatory.
We also examined the 22-year time series of differential photometry
acquired with the T4 0.75m APT at Fairborn Observatory, shown in
Figure 1(c). These measurements, made in the Stroemgren b (467nm) and
y (547nm) bands, are a difference with respect to the mean brightness
of two stable comparison stars, HD 31414 and HD 30606.
Objects:
------------------------------------------------------------
RA (ICRS) DE Designation(s) (Period)
------------------------------------------------------------
04 47 36.29 -16 56 04.0 HD 30495 = HIP 22263 (P=11.3)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 33 1285 S-index observations of HD 30495
table4.dat 56 2001 Photometric observations of HD 30495
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See also:
I/311 : Hipparcos, the New Reduction (van Leeuwen, 2007)
J/A+A/551/L8 : Chromospheric activity of field stars (Pace, 2013)
J/ApJ/763/L26 : SMARTS observations of eps Eridani (Metcalfe+, 2013)
J/A+A/531/A8 : Activity indexes and velocities for 890 stars (Jenkins+, 2011)
J/ApJ/725/875 : Chromospheric activity for CPS stars (Isaacson+, 2010)
J/A+A/520/A79 : FGK stars chromospheric activity (Martinez-Arnaiz+, 2010)
J/AJ/138/312 : Activity of bright solar analogs (Hall+, 2009)
J/A+A/483/903 : Mount Wilson index for FGK stars (Buccino+, 2008)
J/A+A/469/309 : Chromospheric activity in late-type stars (Cincunegui+, 2007)
J/AJ/132/161 : NStars project: The southern sample. I. (Gray+, 2006)
J/ApJS/152/261 : Chromospheric Ca II emission in nearby stars (Wright+, 2004)
J/A+A/365/545 : Remnant disks around MS stars IR flux (Habing+, 2001)
J/ApJ/457/L99 : 25yr CaII-HK obs. of F-K nearby stars (Baliunas+, 1996)
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.4 d HJD [39787.4/56965.8] Heliocentric Julian Date;
HJD-2400000
12- 18 F7.5 --- S [0.24/0.39] The S-index (1)
20- 26 F7.5 --- e_S [0.0004/0.04] The 1-sigma uncertainty in S
28- 33 A6 --- Inst Instrument used (CPS, HARPS, MWO, SMARTS or
SSS)
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Note (1): This dimensionless index is defined as the ratio of the core emission
in the Fraunhofer H and K lines of CaII with the nearby continuum
regions, as measured by the HKP-1 and later HKP-2 photometers at MWO
(Wilson 1968ApJ...153..221W 1968ApJ...153..221W; Vaughan et al. 1978PASP...90..267V 1978PASP...90..267V).
See figure 1.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 10 F10.4 d HJD [49239.9/57080.7] Heliocentric Julian Date;
HJD-2400000
12- 18 F7.4 mag (P-C1)b [-0.5/-0.3] HD30495-HD31414 differential mag in b
20- 26 F7.4 mag (P-C1)y [-0.3/-0.1] HD30495-HD31414 differential mag in y
28- 34 F7.4 mag (P-C2)b [-0.3/-0.1] HD30495-HD30606 differential mag in b
36- 42 F7.4 mag (P-C2)y [-0.3/-0.2] HD30495-HD30606 differential mag in y
44- 50 F7.4 mag (C2-C1)b [-0.2/-0.1] HD30606-HD31414 differential mag in b
52- 56 F5.4 mag (C2-C1)y [0.04/0.08] HD30606-HD31414 differential mag in y
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 01-Feb-2016