J/ApJ/835/25 Calibrated solar S-index time series (Egeland+, 2017)
The Mount Wilson Observatory S-index of the Sun.
Egeland R., Soon W., Baliunas S., Hall J.C., Pevtsov A.A., Bertello L.
<Astrophys. J., 835, 25-25 (2017)>
=2017ApJ...835...25E 2017ApJ...835...25E (SIMBAD/NED BibCode)
ADC_Keywords: Sun
Keywords: stars: activity; Sun: activity; Sun: chromosphere
Abstract:
The most commonly used index of stellar magnetic activity is the
instrumental flux scale of singly ionized calcium H & K line core
emission, S, developed by the Mount Wilson Observatory (MWO) HK
Project, or the derivative index R'HK. Accurately placing the Sun on
the S scale is important for comparing solar activity to that of the
Sun-like stars. We present previously unpublished measurements of the
reflected sunlight from the Moon using the second-generation MWO HK
photometer during solar cycle 23 and determine cycle minimum
S23,min=0.1634±0.0008, amplitude ΔS23=0.0143±0.0012, and
mean <S23≥0.1701±0.0005. By establishing a proxy relationship
with the closely related National Solar Observatory Sacramento Peak
calcium K emission index, itself well correlated with the Kodaikanal
Observatory plage index, we extend the MWO S time series to cover
cycles 15-24 and find on average <Smin≥0.1621±0.0008,
<ΔScyc≥0.0145±0.0012, <Scyc≥0.1694±0.0005. Our
measurements represent an improvement over previous estimates that
relied on stellar measurements or solar proxies with non-overlapping
time series. We find good agreement from these results with
measurements by the Solar-Stellar Spectrograph at Lowell Observatory,
an independently calibrated instrument, which gives us additional
confidence that we have accurately placed the Sun on the S-index flux
scale.
Description:
The Mount Wilson HK Program observed the Moon with both the HKP-1 and
HKP-2 instruments. After removing 11 obvious outliers, there are 162
HKP-1 observations taken from 1966 September 2 to 1977 June 4 with the
Mount Wilson 100 inch reflector, covering the maximum of cycle 20 and
the cycle 20-21 minimum.
As mentioned in Baliunas+ (1995ApJ...438..269B 1995ApJ...438..269B), observations of the
Moon resumed in 1993 with the HKP-2 instrument. After removing 10
obvious outliers, there are 75 HKP-2 observations taken from 1994
March 27 to 2002 November 23 with the Mount Wilson 60 inch reflector,
covering the end of cycle 22 and the cycle 23 minimum, extending just
past the cycle 23 maximum. The end of observations coincides with the
unfortunate termination of the HK Project in 2003.
We seek to extend our time series of solar variability beyond cycle 23
by establishing a proxy to the NSO Sacramento Peak (NSO/SP)
observations taken from 1976 to 2016, covering cycles 21 to 24. The
spectral intensity scale is set by integrating a 0.53Å band
centered at 3934.869Å in the K-line wing and setting it to the
fixed value of 0.162.
We extend the S-index record back to cycle 20 using the composite K
time series of Bertello+ (2016SoPh..291.2967B 2016SoPh..291.2967B).
See section 3 for further explanations.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 37 6349 Calibrated solar S-index time series
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See also:
III/159 : Ca II H and K Measurements Made at MWO (Duncan+ 1991)
J/ApJ/416/787 : Mount Wilson Crv Metallicity index (Soon+ 1993)
J/ApJ/457/L99 : 25yr CaII-HK obs. of F-K nearby stars (Baliunas+, 1996)
J/PASP/108/313 : Empirical stellar flux scales (Hall 1996)
J/ApJ/687/1264 : Age estimation for solar-type dwarfs (Mamajek+, 2008)
J/AJ/138/312 : Activity of bright solar analogs (Hall+, 2009)
J/ApJ/812/12 : S-index and Stroemgren LC of HD30495 (Egeland+, 2015)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 9 F9.3 d JD Julian Date; JD-2400000
11- 18 F8.6 --- OrgSK [0.08/0.2] Orignal S or K index
20- 27 F8.6 --- CalS [0.1/0.2] Calibrated S index
29- 37 A9 --- Inst Instrument used (1)
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Note (1): Instrument as follows:
MWO/HKP-1 = Mount Wilson Observatory (MWO) HKP-1 instrument (162 occurrences);
see section 3.1.
MWO/HKP-2 = Mount Wilson Observatory (MWO) HKP-2 instrument (75 occurrences)
see section 3.1.
NSO/SP = National Solar Observatory Sacramento Peak (4112 occurrences);
see sections 3.2. and 3.3.
SSS/CCD-1 = Solar-Stellar Spectrograph (SSS) at Lowell Observatory
(1241 occurrences); see section 3.4.
SSS/CCD-2 = Solar-Stellar Spectrograph (SSS) at Lowell Observatory
(759 occurrences); see section 3.4
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 02-Aug-2017