J/ApJ/855/75 24 years monitoring of Sun and Sun-like stars (Radick+, 2018)
Patterns of variation for the Sun and Sun-like stars.
Radick R.R., Lockwood G.W., Henry G.W., Hall J.C., Pevtsov A.A.
<Astrophys. J., 855, 75 (2018)>
=2018ApJ...855...75R 2018ApJ...855...75R
ADC_Keywords: Sun; Stars, G-type; Photometry; Optical; Spectroscopy
Keywords: stars: activity ; stars: solar-type ; Sun: activity
Abstract:
We compare patterns of variation for the Sun and 72 Sun-like stars by
combining total and spectral solar irradiance measurements between
2003 and 2017 from the SORCE satellite, Stromgren b, y stellar
photometry between 1993 and 2017 from Fairborn Observatory, and solar
and stellar chromospheric CaII H+K emission observations between 1992
and 2016 from Lowell Observatory. The new data and their analysis
strengthen the relationships found previously between chromospheric
and brightness variability on the decadal timescale of the solar
activity cycle. Both chromospheric H+K and photometric b, y
variability among Sun-like stars are related to average chromospheric
activity by power laws on this timescale. Young active stars become
fainter as their H+K emission increases, and older, less active, more
Sun-age stars tend to show a pattern of direct correlation between
photometric and chromospheric emission variations. The directly
correlated pattern between total solar irradiance and chromospheric Ca
ii emission variations shown by the Sun appears to extend also to
variations in the Stromgren b, y portion of the solar spectrum.
Although the Sun does not differ strongly from its stellar age and
spectral class mates in the activity and variability characteristics
that we have now studied for over three decades, it may be somewhat
unusual in two respects: (1) its comparatively smooth, regular
activity cycle, and (2) its rather low photometric brightness
variation relative to its chromospheric activity level and variation,
perhaps indicating that facular emission and sunspot darkening are
especially well-balanced on the Sun.
Description:
Starting in the late 1970s, variations in total solar irradiance (TSI)
have been monitored by radiometers aboard a series of spacecraft,
including the Total Irradiance Monitor (TIM) instrument on the SOlar
Radiation and Climate Experiment (SORCE) satellite from 2003 to the
present.
Observations to monitor relatively bright stars very similar to the
Sun have been made with the Solar-Stellar Spectrograph (SSS) at Lowell
Observatory and automatic photometric telescopes (APTs) at Fairborn
Observatory beginning in 1992 and 1993, respectively. In all, 72
stars, including 18 from the broader R98-L07 (1998ApJS..118..239R 1998ApJS..118..239R and
2007ApJS..171..260L 2007ApJS..171..260L) sample, have been observed at both locations,
some for as long as 24 seasons. These joint observations provide the
primary stellar data for this paper.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 50 73 Stellar sample
table3.dat 50 73 Lowell/Solar-Stellar Spectrograph (SSS)
spectroscopic results
table4.dat 111 1800 Seasonal data file
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See also:
II/5 : UBV Photometry of Bright Stars (Johnson+ 1966)
II/215 : uvby-beta Catalogue (Hauck+ 1997)
I/239 : The Hipparcos and Tycho Catalogues (ESA 1997)
J/A+AS/102/89 : uvby-beta Photometry of G5 stars (Olsen 1993)
J/A+AS/104/429 : uvby Photometry of G-type dwarfs (Olsen 1994)
J/ApJ/687/1264 : Age estimation for solar-type dwarfs (Mamajek+, 2008)
J/AJ/138/312 : Activity of bright solar analogs (Hall+, 2009)
J/ApJS/211/24 : Rotation periods of Kepler MS stars (McQuillan+, 2014)
J/MNRAS/446/2959 : Asterosismology for solar analogues 16 Cyg (Davies+, 2015)
J/ApJ/812/12 : S-index and Stroemgren LC of HD30495 (Egeland+, 2015)
J/ApJ/835/25 : Calibrated solar S-index time series (Egeland+, 2017)
J/ApJ/851/116 : Variability of Kepler sun-like stars (Montet+, 2017)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Name HD identifier or "Sun"
8-11 F4.2 mag Vmag [3.4/8.7]? V-band magnitude from I/239
13-16 F4.2 mag VMag [2/8.4] Absolute V-band magnitude (MV)
18-22 F5.3 mag B-V [0.4/1.4] B-V color index from I/239
24-31 A8 --- SpT MK spectral type from VizieR and SIMBAD
33-37 F5.2 [-] logR'HK [-5.3/-4.3] logR'HK value (1)
39-42 F4.2 --- Metric [0/7.6] Metric (2)
44-50 A7 --- Notes Notes (3)
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Note (1): log(R'HK) (Noyes+ 1984ApJ...279..763N 1984ApJ...279..763N) measures
the fraction of a star's luminosity that appears as chromospheric H+K
emission. These values were computed using the B-V colors from column
4 and long-term SSS S-indices from this work ("MeanS"), and therefore
should be relatively self-consistent.
Note (2): Values for a metric previously devised (R98; 1998ApJS..118..239R 1998ApJS..118..239R) to
quantitatively assess a star as a solar analog by measuring its
distance from the Sun in a three-dimensional MV, B-V, logR'HK,
weighting equally distances of 1.0mag in MV, 0.1mag in B-V and 0.2
in logR'HK (about 0.05 in the Mount Wilson S-index). In the R98 and
L07 (2007ApJS..171..260L 2007ApJS..171..260L) studies, the closest matches to the Sun
according to this metric were over a unit away. In contrast, 30 stars
of the present sample are less than one unit distant from the Sun, and
the closest, HD 146233, is only 0.13 unit away, confirming its status
as a "solar twin."
Note (3): Stars that were included in previous studies as follows:
E = ELODIE (Soubiran & Triaud 2004A&A...418.1089S 2004A&A...418.1089S),
H = H07 (Hall+ 2007AJ....133..862H 2007AJ....133..862H),
L = L07 (Lockwood+ 2007ApJS..171..260L 2007ApJS..171..260L), and
M = Mount Wilson HK program (Lockwood+ 1997ApJ...485..789L 1997ApJ...485..789L ;
Radick+ 1998ApJS..118..239R 1998ApJS..118..239R and Lockwood+ 2007ApJS..171..260L 2007ApJS..171..260L).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Name HD identifier or "Sun"
8-16 A9 yr Dates Date range (total span of the measurements)
18-19 I2 --- N [1/23] Nn>5 (4)
21-26 F6.4 --- MeanS [0.1/0.8] Mean long-term SSS S-index
28-33 F6.4 --- e_MeanS [0.0003/0.1]? σS value
35-41 F7.4 --- d/dS [-0.9/1.1]? d(mag)/dS
43 I1 --- n_d/dS [1]? Note on d/dS (5)
45-50 F6.4 --- SE [0.003/0.8]? SE slope
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Note (4): Nn>5 is the number of seasons used for regressions of seasonal
mean (b+y)/2 mag on S-index, further discussed in Section 5.
Note (5):
1 = Regression of TSI (in magnitude units) on S-index for the Sun.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Name Henry Draper Catalog number
8- 14 F7.2 yr APTEpoch [1993.3/2016.98]? APT mid-season epoch
16- 18 I3 --- Nobs [6/305]? Number of photometric observations
20- 26 F7.4 mag P-Cavg [-0.03/0.04]? Program star - mean comp. star
magnitude (1)
28- 34 F7.4 mag B_P-Cavg [-0.009/-0.0001]? Upper 95% confidence interval
in (P-Cavg)
36- 42 F7.4 mag b_P-Cavg [0.0001/0.02]? Lower 95% confidence interval
in (P-Cavg)
44- 50 F7.4 mag C2-C3 [-0.02/0.007]? Comp. 2 - comp. 3 magnitude (1)
52- 58 F7.4 mag B_C2-C3 [-0.004/-0.0001]? Upper 95% confidence interval
in C2-C3
60- 66 F7.4 mag b_C2-C3 [0.0001/0.004]? Lower 95% confidence interval
in C2-C3
68- 74 F7.2 yr SSSEpoch [1992.7/2016.9]? SSS mid-season epoch
76- 77 I2 --- NS [1/78]? Number of S index observations
79- 85 F7.4 --- S [0.1/1]? Seasonal median S index
87- 93 F7.4 --- B_S [0.0001/0.2]? Upper 95% confidence interval in S
95-101 F7.4 --- b_S [-0.4/-0.0001]? Lower 95% confidence interval
in S
103-108 F6.3 [-] logR'HK [-5.4/-4.3]? Seasonal median logR'HK
110-111 I2 --- Season [1/25] Season number beginning with 1992-93
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Note (1): Seasonal (b+y)/2 tri-mean, relative to grand mean of
all photometric observations.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 03-Jan-2019