J/ApJ/936/L23 T4 APT photometry of HD 166620 (Luhn+, 2022)
HD 166620: Portrait of a Star Entering a Grand Magnetic Minimum.
Luhn J.K., Wright J.T., Henry G.W., Saar S.H., Baum A.C.
<Astrophys. J., 936, L23 (2022)>
=2022ApJ...936L..23L 2022ApJ...936L..23L
ADC_Keywords: Stars, high-velocity; Photometry, VRI
Keywords: Stellar activity ; Maunder minimum ; Solar cycle
Abstract:
HD-166620 was recently identified as a Maunder minimum candidate based
on nearly 50 years of CaII H and K activity data from Mount Wilson and
Keck HIRES. These data showed clear cyclic behavior on a 17yr
timescale during the Mount Wilson survey that became flat when picked
up later with Keck HIRES planet-search observations. Unfortunately,
the transition between these two data sets-and therefore the
transition into the candidate Maunder minimum phase-contained little
to no data. Here, we present additional Mount Wilson data not present
in Baum et al., along with photometry over a nearly 30yr baseline that
definitively traces the transition from cyclic activity to a prolonged
phase of flat activity. We present this as conclusive evidence of the
star entering a grand magnetic minimum and therefore the first true
Maunder minimum analog. We further show that neither the overall
brightness nor the chromospheric activity level (as measured by SHK)
is significantly lower during the grand magnetic minimum than its
activity cycle minimum, implying that an anomalously low mean or
instantaneous activity levels are not a good diagnostic or criterion
for identifying additional Maunder minimum candidates. Intraseasonal
variability in SHK, however, is lower in the star's grand minimum;
this may prove a useful symptom of the phenomenon.
Description:
We acquired 1278 photometric observations of HD166620 covering 17
observing seasons from 1993 to 2020 (we did not observe the star
during the 2005 through 2015 observing seasons). The observations were
all obtained with the T4 0.75m automatic photoelectric telescope (APT)
at Fairborn Observatory in southern Arizona. The T4 APT is equipped
with a single channel photometer that uses an EMI 9124QB bi-alkali
photomultiplier tube to measure stellar brightness successively in the
Stromgren b and y passbands.
Objects:
-------------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------------
18 09 37.41 +38 27 27.9 HD 166620 = ** LUH 13A
-------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 40 1885 All SHK activity data
table3.dat 33 1278 T4 APT photometry
--------------------------------------------------------------------------------
See also:
J/AJ/111/439 : Chromospheric emission in late-type stars. (Henry+ 1996)
J/A+A/417/651 : NEXXUS ROSAT survey of coronal X-ray (Schmitt+, 2004)
J/ApJS/152/261 : Chromospheric Ca II emission in nearby stars (Wright+, 2004)
J/ApJ/725/875 : Chromospheric activity for CPS stars (Isaacson+, 2010)
J/ApJS/225/32 : Extended abundance analysis of cool stars (Brewer+, 2016)
J/ApJ/874/107 : HARPS-N solar radial velocities & activity (Milbourne+, 2019)
J/ApJ/904/140 : Ruprecht147 members & rot. data 5 other cl. (Curtis+, 2020)
J/AJ/163/183 : S-value for 59 Sun-like starswith HIRES and HKP (Baum+, 2022)
J/AJ/163/180 : RVel & BV photometry of 9 γ Doradus stars (Henry+, 2022)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.2 d JD [2439342/2458918] Julian Date
12- 21 F10.5 yr Year [1966/2021] Fractional year
23- 32 F10.8 --- SHK [0.14/0.88] The SHK activity index
34- 40 A7 --- Inst Instrument identifier (1)
--------------------------------------------------------------------------------
Note (1): Instruments as follows:
MW = Mount Wilson HK photometer through June 4, 1995, from Baum+,
2022, J/AJ/163/183, originally obtained through National Solar
Observatory Archives: "HKProjectv1995_NSO" of Radick & Pevtsov
(2018, http://doi.org/10.7910/DVN/ZRJ6NT).
HIRES = Keck-HIRES.
new_MW = Mount Wilson HK photometer after June 4, 1995, as given in
Olah+, 2016A&A...590A.133O 2016A&A...590A.133O, via private comm.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.2 d JD [2449094/2459156] Julian Date
12- 21 F10.5 yr Year [1993/2021] Fractional year
23- 28 F6.4 mag mag [0.76/0.78] Differential magnitude (1)
30- 33 A4 --- Inst Instrument identifier (2)
--------------------------------------------------------------------------------
Note (1): Where the differential magnitude is HD166620 minus the "b"
comparison star. To improve the photometric precision of the
individual nightly observations, we combine the differential
b and y magnitudes into a single (b+y)/2 "passband."
Note (2): All observations were obtained with the T4 0.75m automatic
photoelectric telescope (APT) at Fairborn Observatory in southern
Arizona. The T4 APT is equipped with a single channel photometer
that uses an EMI 9124QB bi-alkali photomultiplier tube to measure
stellar brightness successively in the Stromgren b and y passbands.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 02-Jul-2024