J/ApJ/928/L8 Infrared LC and spectrum of Scutum X-1 system (De+, 2022)
A massive AGB donor in Scutum X-1: identification of the first Mira variable in
an X-ray binary.
De K., Chakrabarty D., Soria R., Ashley M.C.B., Conroy C., Hankins M.J.,
Kasliwal M.M., Lau R.M., Moore A.M., Simcoe R., Soon J., Travouillon T.
<Astrophys. J., 928, L8 (2022)>
=2022ApJ...928L...8D 2022ApJ...928L...8D
ADC_Keywords: Stars, variable; Binaries, X-ray; Spectra, infrared; Photometry;
Stars, giant
Keywords: X-ray binary stars ; Mira variable stars ; Sky surveys ;
Asymptotic giant branch
Abstract:
The symbiotic X-ray binary Sct X-1 was suggested to be the first known
neutron star accreting from a red supergiant companion. Although known
for nearly 50yr, detailed characterization of the donor remains
lacking, particularly due to the extremely high reddening toward the
source (AV≳25mag). Here, we present (i) improved localization of
the counterpart using Gaia and Chandra observations, (ii) the first
broadband infrared spectrum (∼1-5µm; R∼2000) obtained with SpeX on
the NASA Infrared Telescope Facility, and (iii) the J-band light curve
from the Palomar Gattini-IR survey. The infrared spectrum is
characterized by (i) deep water absorption features (H2O index
∼40%), (ii) strong TiO, VO, and CO features, and (iii) weak/absent CN
lines. We show that these features are inconsistent with known red
supergiants but suggest an M8-9 III-type O-rich Mira donor star. We
report the discovery of large-amplitude (ΔJ∼3.5mag) periodic
photometric variability, suggesting a pulsation period of
621±36 (systematic) ±8 (statistical) days, which we use to
constrain the donor to be a relatively luminous Mira
(MK=-8.6±0.3mag) at a distance of 3.6-0.7+0.8kpc. Comparing
these characteristics to recent models, we find the donor to be
consistent with a ∼3-5M☉ star at an age of ∼0.1-0.3Gyr.
Together, we show that Sct X-1 was previously misclassified as an
evolved high-mass X-ray binary; instead, it is an intermediate-mass
system with the first confirmed Mira donor in an X-ray binary. We
discuss the implications of Mira donors in symbiotic X-ray binaries
and highlight the potential of wide-field infrared time-domain surveys
and broadband infrared spectroscopy to unveil their demographics.
Description:
Palomar Gattini-IR is a wide-field (∼25deg2) and shallow J-band
survey, monitoring the entire visible sky from Palomar Observatory
using a 30cm telescope with a cadence of ∼2 nights. The light curve of
2MASS J18352582-0736501 is shown in Figure 1 and was binned over ∼7d
intervals to improve the signal-to-noise ratio.
We obtained an infrared spectrum of 2MASSJ18352582-0736501 using SpeX
on the NASA Infrared Telescope Facility (Program 2021A083, PI: De) on
UT 2021-May-16. The data were obtained with a 0.3" slit, in both the
SXD and LXD_long modes over multiple dithered exposures amounting to a
total exposure time of ∼720s and ∼300s, respectively. The combined
spectrum covers the full wavelength range of the instrument from
∼0.8 to ∼5.0um with a resolution of R∼2000.
The Chandra X-ray Observatory observed Sct X-1 on 2020-Nov-09
(ObsID 22417). See section 2.3.
Objects:
----------------------------------------------------------------
RA (ICRS) DE Designation(s)
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18 35 25.82 -07 36 50.4 2MASS J18352582-0736501 = X Sct X-1
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
fig1.dat 22 54 Palomar Gattini-IR (PGIR) J-band light curve
of 2MASS J18352582-0736501
fig2.dat 23 13059 SpeX SXD and LXD_long spectra
of 2MASS J18352582-0736501
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
II/195 : Namelists of variable stars Nos.67-73 (Khopolov+, 1985-97)
III/114 : Spectra of Late-Type Standards, 2.0-2.5 Microns (Kleinmann+ 1986)
III/196 : Near-IR stellar spectra from 1.428 to 2.5 um (Lancon+ 1996)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/A+AS/146/217 : Library of Sp. (0.5 to 2.5um) of Cool Stars (Lancon+ 2000)
J/ApJ/597/323 : Cool stars at the Galactic Center (Blum+, 2003)
J/A+A/425/489 : Late-type stars in the inner Milky Way (Comeron+, 2004)
J/MNRAS/376/313 : Carbon star in Magellanic Cloud (Groenewegen+, 2007)
J/MNRAS/386/313 : IR observations of Mira variables (Whitelock+, 2008)
J/AJ/152/164 : I-band light curves of OGLE LMC Miras (He+, 2016)
J/ApJS/240/21 : Symbiotic stars with 2MASS, WISE & Gaia data (Akras+, 2019)
J/MNRAS/483/5077 : Machine learning to identify symbiotic stars (Akras+, 2019)
J/ApJ/872/43 : IR sp. of symbiotic stars. XII. V934 Her (Hinkle+, 2019)
J/A+A/634/A133 : X-Shooter Spectral Library (XSL). DR2 (Gonneau+, 2020)
J/ApJS/257/23 : Multiwavelength obs. of Miras in the LMC (Iwanek+, 2021)
J/AJ/162/187 : IRTF spectral indices for giant stars (Messineo+, 2021)
Byte-by-byte Description of file: fig1.dat
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Bytes Format Units Label Explanations
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1- 9 F9.3 d MJD [58425.1/59448.4] Modified Julian Date
(JD-2400000.5)
11- 16 F6.3 mag Jmag [10.27/14.16] PGIR J-band magnitude
18- 22 F5.3 mag e_Jmag [0.02/1.3] Uncertainty in Jmag
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Byte-by-byte Description of file: fig2.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- Mode Spex Mode, SXD or LXD_long
5- 12 F8.2 0.1nm lambda [9187.3/53689] Wavelength, Angstroms
14- 23 E10.3 mW/m2 Flux [-2.9e-12/4.3e-12] Flux density, erg/s/cm2
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 04-Mar-2024