J/AJ/165/188 Blue Straggler Stars in the Open Cluster NGC 6819 (Guzik+, 2023)
Variable Blue Straggler Stars in the Open Cluster NGC 6819 Observed in the
Kepler "Superstamp" Field
Guzik J.A., Baran A.S., Sanjayan S., Nemeth P., Hedlund A.M.,
Jackiewicz J., Dauelsberg L.R.
<Astron. J., 165, 188 (2023)>
=2023AJ....165..188G 2023AJ....165..188G
ADC_Keywords: Clusters, open; Stars, variable; Stars, blue; Spectra, optical
Keywords: Delta Scuti variable stars ; Asteroseismology ; Blue straggler
stars ; Pulsating variable stars ; Gamma Doradus variable
stars ; Stellar evolution
Abstract:
NGC6819 is an open cluster of age 2.4Gyr that was in the NASA Kepler
spacecraft's field of view from 2009 to 2013. The central part of the
cluster was observed in a 200x200pixel "superstamp" during these four
years in 30minute cadence photometry, providing a unique,
high-precision, long time-series data set. The cluster contains "blue
straggler" stars, i.e., stars on the main sequence above the cluster
turnoff that should have left the main sequence to become red giants.
We present light curves and pulsation frequency analyses derived from
custom photometric reductions for five confirmed cluster members-four
blue stragglers and one star near the main-sequence turnoff. Two of
these stars show a rich spectrum of δScuti pulsation modes, with
236 and 124 significant frequencies identified, respectively, while
two stars show mainly low-frequency modes, characteristic of
γDoradus variable stars. The fifth star, a known active X-ray
binary, shows only several harmonics of two main frequencies. For the
two δScuti stars, we use a frequency separation-mean density
relation to estimate their mean densities, and then use these values
along with their effective temperature to derive their stellar masses
and radii. For the two stars showing low frequencies, we searched for
period-spacing sequences that may be representative of gravity-mode or
Rossby-mode sequences, but found no clear sequences. The common age
for the cluster members, considered along with the frequencies, will
provide valuable constraints for asteroseismic analyses, and may shed
light on the origin of the blue stragglers.
Description:
We did not find stellar parameters derived from spectroscopy for these
five stars in the literature, for example, from the LAMOST ROTFIT
pipeline. We have taken new low-resolution spectra (R∼2000) for three
of the stars, KIC5024468, KIC5113357, and KIC5112843, using the
Alhambra Faint Object Spectrograph and Camera (ALFOSC) spectrograph
mounted on the 2.56m Nordic Optical Telescope (NOT) at the Roque de
los Muchachos Observatory on La Palma.
Objects:
------------------------------------------------
RA (ICRS) DE Designation(s)
------------------------------------------------
19 41 18.48 +40 11 23.9 NGC 6819 = C 1939+400
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 188 5 Summary of the properties of the five NGC6819
stars observed in the Kepler Superstamp field
tablea1.dat 108 512 Significant frequencies for KIC 5024468, 5024084,
5024455, 5113357, 5112843
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See also:
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
IV/38 : TESS Input Catalog - v8.0 (TIC-8) (Stassun+, 2019)
J/ApJ/729/L10 : KIC stars properties in NGC 6791 and NGC 6819 (Basu+, 2011)
J/A+A/534/A125 : Variability of A- & F-stars from Kepler (Uytterhoeven+ 2011)
J/MNRAS/427/2180 : GALEX survey subdwarf atmospheric parameters (Nemeth+, 2012)
J/AJ/148/38 : WIYN open cluster LX. RV survey of NGC6819 (Milliman+, 2014)
J/A+A/583/A65 : Active Kepler stars differential rotation (Reinhold+, 2015)
J/A+A/574/A17 : Period spacings in gamma Dor stars (Van Reeth+, 2015)
J/AJ/151/66 : Velocities WOCS24009 & WOCS40007 in NGC6819 (Brewer+, 2016)
J/ApJS/224/41 : Frequency spacing of δScuti stars. II. (Paparo+, 2016)
J/A+A/614/A46 : delta Scuti stars Teff-νmax (Barcelo Forteza+, 2018)
J/MNRAS/490/4040 : δScuti & γDoradus stars in TESS (Antoci+, 2019)
J/AJ/158/163 : Li abundance values for stars in NGC6819 (Deliyannis+, 2019)
J/MNRAS/491/3586 : 611 γ Doradus stars Kepler data (Li+, 2020)
J/A+A/650/A67 : Blue & yellow straggler stars in open clusters (Rain+, 2021)
J/ApJS/258/39 : Kepler IRIS cat LCs NGC6791 & NGC6819 fields (Colman+, 2022)
J/AcA/72/77 : Variable star population in NGC 6791 (Sanjayan+, 2022)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- KIC KIC identifier
9 A1 --- f_KIC Flag on KIC (1)
11- 19 A9 --- Ref Reference(s) used (2)
21- 31 F11.7 deg RAdeg [295/296] Degree of right ascension (J2000)
33- 43 F11.8 deg DEdeg [40/41] Degree of declination (J2000)
45- 54 I10 --- TIC TIC identifier
56- 61 F6.3 mag Vmag [12.9/15.8] V-band magnitude
63- 67 F5.3 mag e_Vmag [0.04/0.2] Error on Vmag
69- 72 I4 K Teff [5493/7328] Effective temperature
74- 76 I3 K e_Teff [122/130] Error on Teff
78- 82 F5.3 cm/s2 logg [3.44/4.25] Surface gravity
84- 88 F5.3 cm/s2 e_logg [0.096]? Error on logg
90- 93 F4.2 Rsun Rad [1.49/3.93] Stellar radius
95- 98 F4.2 Rsun e_Rad [0.26]? Error on Rad
100-103 F4.2 Msun Mass [0.96/1.66] Stellar mass
105-108 F4.2 Msun e_Mass [0.25]? Error on Mass
110-115 F6.3 Lsun Lum [3.6/34.6] Stellar luminosity
117-120 F4.2 Lsun e_Lum [4.03]? Error on Lum
122-147 A26 --- SpT H-R diagram location
149-151 I3 --- Nfreq [17/236] Number of frequency
153-188 A36 --- Class Classification
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Note (1): Flags as follows:
a = Light curve contaminated by KIC5024450
b = Single-line spectroscopic binary, 762 day orbital period according to
Milliman+, 2014, J/AJ/148/38
c = Eclipsing binary, 0.3487 day orbital period according to
Talamantes+, 2010AJ....140.1268T 2010AJ....140.1268T
Note (2): References as follows:
1 = SIMBAD
2 = Talamantes+, 2010AJ....140.1268T 2010AJ....140.1268T
3 = Colman, 2020PhDT........26C 2020PhDT........26C
4 = Balona+, 2013MNRAS.430.3472B 2013MNRAS.430.3472B
5 = Reinhold & Gizon, 2015, J/A+A/583/A65
6 = Uytterhoeven+, 2011, J/A+A/534/A125
7 = Milliman+, 2014, J/AJ/148/38
8 = Gosnell+, 2012ApJ...745...57G 2012ApJ...745...57G
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 7 I7 --- KIC Kepler Input Catalog number (1)
9- 13 A5 --- FN Frequency Number (2)
15- 25 F11.8 --- Freq1 [0.07/36.5] Frequency, c/d
27- 36 F10.8 --- e_Freq1 [1e-07/0.0004]? Uncertainty in Freq1, c/d
38- 48 F11.7 uHz Freq2 [0.87/423] Frequency
50- 58 F9.7 uHz e_Freq2 [1.2e-06/0.005]? Uncertainty in Freq2
60- 72 F13.10 d Per [0.02/13.2] Period
74- 85 F12.10 d e_Per [1e-09/0.002]? Uncertainty in Per
87- 93 F7.4 10-3 Amp [0.018/21.4] Amplitude, parts per thousand
95-100 F6.4 10-3 e_Amp [0.003/0.03] Uncertainty in Amp parts per thousand
102-108 F7.2 --- SNR [4.18/3881] Signal-to-Noise Ratio
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Note (1): Notes on individual sources
KIC 5024468 = The harmonics of the 3.05day eclipsing binary
signal are removed from this table
KIC 5113357 = The first frequency in the table (f1) has the
second-highest amplitude, and 3 of its harmonics, listed
next, are found in the amplitude spectrum. This frequency may
be a binary orbital frequency, and KIC5113357 may be a
contact eclipsing binary;
KIC 5112843 = The spectrum shows only harmonics of the two lowest
frequencies. The average background noise level in the
residual after pre-whitening these frequencies is 0.0055ppt,
with higher noise level at lower frequencies.
Note (2): Real super-Nyquist frequencies are flagged by asterisks; harmonics
precede the FN delimited by a colon, e.g., 2:f1 is the second harmonic
of the f1 FN.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 15-Sep-2023