J/ApJ/940/19 Spectrophotometric standard DA white dwarfs (Calamida+, 2022)
Perfecting our set of spectrophotometric standard DA white dwarfs.
Calamida A., Matheson T., Olszewski E.W., Saha A., Axelrod T.,
Shanahan C., Holberg J., Points S., Narayan G., Malanchev K.,
Ridden-Harper R., Gentile-Fusillo N., Raddi R., Bohlin R., Rest A.,
Hubeny I., Deustua S., Mackenty J., Sabbi E., Stubbs C.W.
<Astrophys. J., 940, 19 (2022)>
=2022ApJ...940...19C 2022ApJ...940...19C
ADC_Keywords: Stars, white dwarf; Spectra, optical; Photometry, HST
Keywords: Flux calibration ; Photometric standard stars ;
Spectrophotometric standards ; Variable stars ; DA stars ;
White dwarf stars ; Time series analysis
Abstract:
We verified for photometric stability a set of DA white dwarfs with
Hubble Space Telescope magnitudes from the near-ultraviolet to the
near-infrared and ground-based spectroscopy by using time-spaced
observations from the Las Cumbres Observatory network of telescopes.
The initial list of 38 stars was whittled to 32 final ones, which
comprise a high-quality set of spectrophotometric standards. These
stars are homogeneously distributed around the sky and are all fainter
than r∼16.5mag. Their distribution is such that at least two of them
would be available to be observed from any observatory on the ground
at any time at airmass less than 2. Light curves and different
variability indices from the Las Cumbres Observatory data were used to
determine the stability of the candidate standards. When available,
Pan-STARRS1, Zwicky Transient Facility, and TESS data were also used
to confirm the star classification. Our analysis showed that four DA
white dwarfs may exhibit evidence of photometric variability, while a
fifth is cooler than our established lower temperature limit, and a
sixth star might be a binary. In some instances, due to the presence
of faint nearby red sources, care should be used when observing a few
of the spectrophotometric standards with ground- based telescopes.
Light curves and finding charts for all the stars are provided.
Description:
Spectra of the Northern sample of DA white dwarfs (DAWDs) were
collected with the Gemini Multi-Object Spectrograph (GMOS) mounted on
the Gemini North and South telescopes. However, due to issues with the
quality of the GMOS spectra, further observations were collected with
the Blue Channel spectrograph at the MMT Observatory. Details on these
data and their reduction and analysis were presented in
Calamida+ 2019, J/ApJ/872/199.
Spectra of 48 Southern candidate WDs were obtained with the Goodman
spectrograph on the 4m SOAR telescope (NOIRLab). Exposures were
collected for each star and some were observed multiple times between
2016 February and 2017 February. The log of the observations is
provided in Table 2.
All the spectra were visually inspected and non-DAWD stars and stars
with obvious spectroscopic peculiarities or magnetic activity were
rejected. We ended up with 15 candidate spectrophotometric standard
DAWDs that we observed with WFC3/HST and monitored for stability with
LCO.
See Section 2.1.
Time-spaced data for 23 candidate spectrophotometric standard DAWDs in
the Northern hemisphere and around the celestial equators were
collected with LCO starting in the fall of 2016 until the summer of
2017, for a total of ∼1yr of observations. A few exposures were also
collected in the first semester of 2018. Observations for the
15 candidates in the Southern hemisphere were collected in a semester
in 2018 and one in 2019. The log of the observations is shown in Table 3.
We downloaded all images collected for our programs from the LCO archive.
All data were collected with the Sinistro 4Kx4K cameras mounted on
the 1m class network of telescopes. This includes Siding Spring
(observatory code, COJ), Sutherland (CPT), Cerro Tololo Cerro Tololo
Inter-American Observatory (LSC), and McDonald (ELP). See Section 3.
For a few DAWDs, the LCO light curves and the different variability
indices were still inconclusive to classify them as fully stable
stars. Therefore, we downloaded the Asteroid Terrestrial-impact Last
Alert System (ATLAS; Heinze+ 2018, J/AJ/156/241) survey data, when
available, for targets with decl. north of -50°. In particular, we
downloaded forced photometry in the cyan (c) and orange (o) filters
for 7 DAWDs in the Northern hemisphere and 4 in the Southern one.
See Section 4.2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 176 38 Gaia DR3 astrometry and photometry for the
candidate spectrophotometric standard DA
white dwarfs
table2.dat 126 55 Log of the observations collected with the Goodman
spectrograph on the 4m-SOAR telescope NOAO
programs 2017A-0052 (PI: Olszewski)
table3.dat 75 1064 Log of the observations collected with LCO during
programs LCO2016B-007, LCO2017AB-002, LCO2018A-002,
LCO2018B-001, and LCO2019-B004 (PI: T. Matheson).
table4.dat 92 38 Spectroscopic and photometric parameters for all
the observed DAWDs
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See also:
III/210 : Spectroscopically Identified White Dwarfs (McCook+, 1999)
II/282 : The SDSS Photometric Catalog, Release 6 (Adelman-McCarthy+, 2007)
III/235 : Spectroscopically Identified White Dwarfs (McCook+, 2008)
I/331 : Absolute Proper motions Outside the Plane (APOP) (Qi+, 2015)
J/AJ/127/477 : Hard X-ray emissions of white dwarfs (Chu+, 2004)
J/A+A/492/277 : Analysis of Collinder 69 stars with VOSA (Bayo+, 2008)
J/ApJS/204/5 : SDSS DR7 white dwarf catalog (Kleinman+, 2013)
J/A+A/568/A22 : Joint analysis of the SDSS-II & SNLS SNe Ia (Betoule+, 2014)
J/MNRAS/457/1988 : White dwarfs in Galactic plane (Raddi+, 2016)
J/MNRAS/469/621 : VST ATLAS white dwarf cand. cat. (Gentile Fusillo+, 2017)
J/MNRAS/472/4173 : Bright white dwarfs for high-speed photometry (Raddi+, 2017)
J/AJ/156/241 : Variable stars measured by ATLAS (Heinze+, 2018)
J/ApJ/872/199 : Cand. spectrophotometric standard DA WDs (Calamida+, 2019)
J/ApJ/874/30 : RRab stars toward Baade's window with DECam (Saha+, 2019)
J/MNRAS/502/5147 : Anomaly detection in the ZTF DR3 (Malanchev+, 2021)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 1 A1 --- Set Hemisphere sample (G1)
3- 12 A10 --- Star Position-based Star Name (JHHMM+DDMM) (G2)
14- 14 A1 --- f_ID [*] Flag excluding star from final network of
spectrophotometric standard DAWDs
16- 27 A12 --- WDFS White Dwarf Flux Standard designation
(WDFS HHMM+DD; J2000)
29- 55 A27 --- OName Alternative Name (G3)
57- 75 I19 --- Gaia Gaia DR3 identifier
77- 78 I2 h RAh Hour of Right Ascension (J2000) (G2)
80- 81 I2 min RAm Minute of Right Ascension (J2000) (G2)
83- 88 F6.3 s RAs Second of Right Ascension (J2000) (G2)
90- 90 A1 --- DE- Sign of the Declination (J2000) (G2)
91- 92 I2 deg DEd Degree of Declination (J2000) (G2)
94- 95 I2 arcmin DEm Arcminute of Declination (J2000) (G2)
97-102 F6.3 arcsec DEs Arcsecond of Declination (J2000) (G2)
104-110 F7.3 mas/yr pmRA [-48.6/143.6] Gaia DR3 proper motion in RA
112-116 F5.3 mas/yr e_pmRA [0.04/0.9] Uncertainty in pmRA
118-124 F7.3 mas/yr pmDE [-76/66.5] Gaia DR3 proper motion in Dec
126-130 F5.3 mas/yr e_pmDE [0.05/0.8] Uncertainty in pmDE
132-136 F5.2 mag Gmag [15.88/19.97] Gaia DR3 G-band magnitude
138-142 F5.2 mag RPmag [16.11/20.25] Gaia DR3 RP band magnitude
144-148 F5.2 mag BPmag [15.77/19.82] Gaia DR3 BP band magnitude
150-176 A27 --- ID Identifier as given in Tables 3 and 4;
column added by CDS
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Star Position-based Star Name (G2)
12- 32 A21 --- OName Alternative Name (G3)
34- 52 I19 --- Gaia Gaia DR3 identifier
54- 55 I2 h RAh Hour of Right Ascension (J2000) (G2)
57- 58 I2 min RAm Minute of Right Ascension (J2000) (G2)
60- 65 F6.3 s RAs Second of Right Ascension (J2000) (G2)
67- 67 A1 --- DE- Sign of the Declination (J2000) (G2)
68- 69 I2 deg DEd Degree of Declination (J2000) (G2)
71- 72 I2 arcmin DEm Arcminute of Declination (J2000) (G2)
74- 79 F6.3 arcsec DEs Arcsecond of Declination (J2000) (G2)
81- 84 I4 yr Obs.Y [2016/2017] Observation date, UTC, year
86- 87 I2 "month" Obs.M Observation date, UTC, numeric month
89- 90 I2 d Obs.D Observation date, UTC, day in month
92- 95 I4 0.1nm lam1 [3850/3870] Wavelength min, Angstroms
97-100 I4 0.1nm lam2 [7100/7150] Wavelength max, Angstroms
102-106 F5.1 deg PA [5/348] Position angle of spectrum, E of N
108-110 F3.1 --- Airmass [1/1.7] Air mass
112-119 A8 --- Std Flux Standard ("Feige110", "Feige67" or "GD71")
121-126 A6 --- ExpTime Exposure time, Seconds or CoaddxSeconds
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 1 A1 --- Set Hemisphere sample (G1)
3- 29 A27 --- ID White Dwarf Flux Standard designation or OName
31- 34 A4 --- Tel LCO Telescope code
36- 37 I2 h RAh Hour of Right Ascension (J2000) (G2)
39- 40 I2 min RAm Minute of Right Ascension (J2000) (G2)
42- 47 F6.3 s RAs Second of Right Ascension (J2000) (G2)
49- 49 A1 --- DE- Sign of the Declination (J2000) (G2)
50- 51 I2 deg DEd Degree of Declination (J2000) (G2)
53- 54 I2 arcmin DEm Arcminute of Declination (J2000) (G2)
56- 60 F5.2 arcsec DEs Arcsecond of Declination (J2000) (G2)
62- 71 F10.4 d MJD [57696.9/58817.1] Modified Julian Date of
Observation (JD-2400000.5)
73- 75 I3 s ExpTime [39/579] Exposure time
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Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 A1 --- Set Hemisphere sample (G1)
3 A1 --- f_ID [*] Flag excluding star from final network
of spectrophotometric standard DAWDs
5- 31 A27 --- ID White Dwarf Flux Standard designation or
OName
33 A1 --- Flag Flag (1)
35- 36 I2 --- Nexp [6/45] Number of exposures
38- 43 F6.3 mag GmagEDR3 [15.88/20] Gaia EDR3 G band magnitude
45- 49 F5.3 mag e_GmagEDR3 [0.001/0.006] Uncertainty in Gmag
51- 54 F4.2 mag sigmaLCO [0.01/0.04] Dispersion in LCO timeseries
56- 59 F4.1 --- chi2 [0.7/16.4] Variable reduced χ2,
Equation 1
61- 64 F4.2 --- IQR [0/0.12] Interquartile range, LCO
time-series (2)
66- 70 F5.2 --- 1/eta [0/33] Von Neumann ratio η, LCO
time-series, Equation 2
72- 75 F4.2 --- IQR-ATLAS [0.05/0.91]? Interquartile range, ATLAS
time-series
77- 81 F5.2 --- 1/eta-ATLAS [0.07/77.25]? Von Neumann ratio η,
ATLAS time-series
83- 92 A10 --- Note Note on IR excess
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Note (1): Flag as follows:
a = We warn the users that these standard star measurements could be
affected by the presence of close red faint neighbors when observed
from the ground.
Note (2): the IQR is calculated as the difference between the median value of
the upper and the lower half of the data points, by excluding the 25%
higher and lower values. See Section 4.1.
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Global notes:
Note (G1): Stars are divided as follows:
N = the Northern and Equatorial sample (23 unique sources)
S = the Southern sample (15 unique sources)
Note (G2): Positions and position-based names are from Gaia DR3 precessed to
equinox J2000.0, no proper motion applied (epoch=2016.0)
Note (G3): ATLAS designate stars observed from the Asteroid Terrestrial-impact
Last Alert System (ATLAS) VLT Survey telescope (VST) survey; SSS
are observed from the SuperCOSMOS Sky Survey (SSS).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 12-Sep-2024