J/AJ/159/61 Optical LCs & spectrum of the RCB star ZTF18abhjrcf (Lee+, 2020)
ZTF18abhjrcf: the first R Coronae Borealis star from the Zwicky Transient
Facility public survey.
Lee C.-H., Matheson T., Soraisam M., Narayan G., Saha A., Stubens C.,
Wolf N.
<Astron. J., 159, 61 (2020)>
=2020AJ....159...61L 2020AJ....159...61L
ADC_Keywords: Photometry, ugriz; Spectra, optical; Stars, variable
Keywords: R Coronae Borealis variable stars ; Sky surveys ;
Time series analysis ; Astrostatistics techniques
Abstract:
R Coronae Borealis stars (RCBs) constitute a rare class of stars that
are hydrogen depleted and carbon enriched, possibly from white dwarf
mergers. RCBs are identified by their stochastic dimming with
photometric variations of as much as eight magnitudes. Hence, the
discoveries of RCBs were heavily biased to the limited regions
monitored by long-term microlensing experiments. However, recent
studies of galactic RCBs have shown that they exhibit distinct
mid-infrared colors originating from their cool circumstellar shells.
The all-sky Wide-field Infrared Survey Explorer (WISE) survey thus
facilitates the identification of RCB candidates. Therefore, combining
the WISE colors with large-area time-domain surveys will enable us to
discover more RCBs. Here we present the results of a first attempt to
identify RCBs in the public Zwicky Transient Facility (ZTF) alert
stream, using the alert broker ANTARES. We identify a candidate RCB
using the infrared color selection by Tisserand+, 2013A&A...551A..77T 2013A&A...551A..77T
and large light curve variations in the optical from ZTF. We then
conduct subsequent observations using the FLOYDS spectrograph at the
Las Cumbres Observatory and confirm ZTF18abhjrcf as a bona fide RCB.
This demonstrates the potential to discover uncharted RCBs as ZTF and
other time-domain surveys continue to operate.
Description:
To search for the aperiodic photometric variations of candidate
R Coronae Borealis stars (RCBs), we use data from the high-cadence,
large-area Zwicky Transient Facility (ZTF) public surveys. Starting
from 2018, ZTF constantly patrols the sky north of decl. <-30deg in
both the g and r band. Equipped with a 47 square degree imager, the
48inch Samuel Oschin Schmidt telescope at the Palomar Observatory can
survey the three quarters of the sky visible from Palomar mountain
every three days. With an exposure time of 30s per frame, ZTF can
deliver a median sensitivity of r∼20.5 mag at a 5σ level.
After identifying ZTF18abhjrcf as a promising RCB candidate, we
performed subsequent spectroscopic follow-up to confirm its nature.
The spectroscopic observations were carried out using the Folded Low
Order whYte-pupil Double-dispersed Spectrograph (FLOYDS) spectrograph
at the Las Cumbres Observatory 2m Faulkes Telescope North on Haleakala
in Hawaii. FLOYDS is a cross-dispersed, low-resolution spectrograph
that can simultaneously cover 320-570nm (second order) and 540-1000nm
(first order). The blue and red end have spectral resolutions of R=400
and 700, with 3.51Angs/pixel and 1.74Angs/pixel, respectively. We
employed a 2.0" slit and obtained 4x300s exposures on 2019 October 22 UT.
Objects:
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RA (2000) DE Designation(s)
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18 42 46.25 -12 54 14.9 ZTF18abhjrcf = ZTF18abhjrcf
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig1.dat 24 52 g and r light curves of ZTF18abhjrcf from the Zwicky
Transient Facility (ZTF) alerts
fig3.dat 18 3009 Faulkes Telescope North/FLOYDS spectrum of ZTF18abhjrcf
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See also:
II/264 : ASAS Variable Stars in Southern hemisphere (Pojmanski+, 2002-2005)
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
J/A+A/353/287 : The R CrB stars (Asplund+, 2000)
J/AJ/134/1877 : Spectropolarimetry of R CrB in 1998-2003 (Kawabata+, 2007)
J/AcA/59/335 : VI light curves of LMC R CBr stars (Soszynski+, 2009)
J/PASP/123/1149 : NSV 11154 BVRI light curves (Kijbunchoo+, 2011)
J/A+A/539/A51 : Catalogue enriched with R CrB stars (Tisserand, 2012)
J/ApJ/747/102 : 12C/13C ratio for 18 galactic R CrB stars (Hema+, 2012)
J/A+A/555/A24 : Aperture-synthesis imaging of Antares (Ohnaka+, 2013)
J/A+A/559/A9 : Neutrinos from GRBs with ANTARES (Adrian-Martinez+ 2013)
J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)
J/other/NewA/51.1 : AS CrB BVRI light curves (Liu+, 2017)
J/AJ/156/148 : Multiwavelength photometry of RCB stars (Montiel+, 2018)
J/MNRAS/482/4174 : Heliocentric radial velocities of R CrB (Feast+, 2019)
J/A+A/635/A14 : New R Coronae Borealis stars (Tisserand+, 2020)
http://antares.noao.edu/ : ANTARES home page
Byte-by-byte Description of file: fig1.dat
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Bytes Format Units Label Explanations
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1- 11 F11.5 d MJD [58336/58749] Modified Julian Date (JD-2400000.5)
13- 17 F5.2 mag mag [14/22] Observed magnitude in Filt
19- 22 F4.2 mag e_mag [0.03/1.7] Uncertainty in mag
24- 24 A1 --- Filt [gr] Filter used; g-band (24 occurrences) or
r-band (23 occurrences)
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Byte-by-byte Description of file: fig3.dat
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Bytes Format Units Label Explanations
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1- 8 F8.2 0.1nm lambda [3300/10183] Wavelength in Angstrom
10- 18 F9.6 --- Flux [-0.03/1.1] Flux, normalized
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 09-Mar-2020