Symbiotic Stars Research Articles

The symbiotic X-ray binaries Sct X-1, 4U 1700+24, and IGR J17329−2731

ABSTRACT Symbiotic X-ray binaries are systems hosting a neutron star accreting form the wind of a late-type companion. These are rare objects and so far only a handful of them are known. One of the most puzzling aspects of the symbiotic X-ray binaries is the possibility that they contain strongly magnetized neutron stars. These are expected to be evolutionary much younger compared to their evolved companions and could thus be formed through the (yet poorly known) accretion induced collapse of a white dwarf. In this paper, we perform a broad-band X-ray and soft γ-ray spectroscopy of two known symbiotic binaries, Sct X−1 and 4U 1700+24, looking for the presence of cyclotron scattering features that could confirm the presence of strongly magnetized NSs. We exploited available Chandra, Swift, and NuSTAR data. We find no evidence of cyclotron resonant scattering features (CRSFs) in the case of Sct X−1 but in the case of 4U 1700+24 we suggest the presence of a possible CRSF at ∼16 keV and its first harmonic at ∼31 keV, although we could not exclude alternative spectral models for the broad-band fit. If confirmed by future observations, 4U 1700+24 could be the second symbiotic X-ray binary with a highly magnetized accretor. We also report about our long-term monitoring of the last discovered symbiotic X-ray binary IGR J17329−2731 performed with Swift/XRT. The monitoring revealed that, as predicted, in 2017 this object became a persistent and variable source, showing X-ray flares lasting for a few days and intriguing obscuration events that are interpreted in the context of clumpy wind accretion.

Low-resolution Optical Spectroscopy of Recently Discovered Accreting-only Symbiotic Star THA 15–31

Abstract Recently, the discovery and characterization of a new accreting-only symbiotic star THA 15–31 was presented. Motivated by the suggestion that the optical spectrum of the star might show the emission lines with higher ionization potential in comparison with previously studied epochs, we have obtained a low-resolution spectrum of this target. The spectrum does not reveal the presence of suggested He ii emission lines. Moreover, the near-UV excess seems to be even less prominent now in comparison with the previous observations, suggesting a decrease in mass transfer and accretion rate. The search for He ii emission lines should be repeated when the accretion rate is higher.

A Massive AGB Donor in Scutum X-1: Identification of the First Mira Variable in an X-Ray Binary

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 50 yr, detailed characterization of the donor remains lacking, particularly due to the extremely high reddening toward the source (A V ≳ 25 mag). Here, we present (i) improved localization of the counterpart using Gaia and Chandra observations, (ii) the first broadband infrared spectrum (≈1–5 μm; 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 ≈ 3.5 mag) 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 (M K = −8.6 ± 0.3 mag) at a distance of 3.6 − 0.7 + 0.8 kpc. Comparing these characteristics to recent models, we find the donor to be consistent with a ≈3–5 M ⊙ star at an age of ≈0.1–0.3 Gyr. 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.

An XMM-Newton EPIC X-Ray View of the Symbiotic Star R Aquarii

Abstract We present the analysis of archival XMM-Newton European Photon Imaging Camera (EPIC) X-ray observations of the symbiotic star R Aquarii. We used the Extended Source Analysis Software package to disclose diffuse soft X-ray emission extending up to 2.′2 (≈0.27 pc) from this binary system. The depth of these XMM-Newton EPIC observations reveals in unprecedented detail the spatial distribution of this diffuse emission, with a bipolar morphology spatially correlated with the optical nebula. The extended X-ray emission shares the same dominant soft X-ray-emitting temperature as the clumps in the jet-like feature resolved by Chandra in the vicinity of the binary system. The harder component in the jet might suggest that the gas cools down; however, the possible presence of nonthermal emission produced by the presence of a magnetic field collimating the mass ejection cannot be discarded. We propose that the ongoing precessing jet creates bipolar cavities filled with X-ray-emitting hot gas that feeds the more extended X-ray bubble as they get disrupted. These EPIC observations demonstrate that the jet feedback mechanism produced by an accreting disk around an evolved, low-mass star can blow hot bubbles, similar to those produced by jets arising from the nuclei of active galaxies.

Discovery of the most luminous quasar of the last 9 Gyr

Abstract We report the discovery of a bright ( $g = 14.5$ mag (AB), $K = 11.9$ mag (Vega)) quasar at redshift $z=0.83$ — the optically brightest (unbeamed) quasar at $z>0.4$ . SMSS J114447.77-430859.3, at a Galactic latitude of $b=+18.1^{\circ}$ , was identified by its optical colours from the SkyMapper Southern Survey (SMSS) during a search for symbiotic binary stars. Optical and near-infrared spectroscopy reveals broad Mg ii, H $\unicode{x03B2}$ , H $\unicode{x03B1}$ , and Pa $\unicode{x03B2}$ emission lines, from which we measure a black hole mass of $\log_{10}\! (M_{\mathrm{BH}}/\mathrm{M}_{\odot}) = 9.4 \pm 0.5$ . With its high luminosity, $L_{\mathrm{bol}} = (4.7\pm1.0)\times10^{47}\,\mathrm{erg\,s}^{-1}$ or $M_{i}(z=2) = -29.74$ mag (AB), we estimate an Eddington ratio of $\approx1.4$ . As the most luminous quasar known over the last ${\sim}$ 9 Gyr of cosmic history, having a luminosity $8\times$ greater than 3C 273, the source offers a range of potential follow-up opportunities.

SU Lyn - a transient symbiotic star

ABSTRACT SU Lyn is a binary system composed of a white dwarf and a red giant star. Although it is known to be bright and variable at X-ray wavelengths, the optical counterpart of the source appeared as a single red giant without prominent emission lines. Because of the lack of optical features typical for interacting systems, the system was classified as a hidden symbiotic star. We present the results of optical monitoring of the system. While SU Lyn did not show substantial photometric variability, the spectroscopic observations revealed a complex behaviour. The system showed strong emission line variability, including P Cygni profiles, changing line emission environments, and variable reddening. Both X-ray and optical observations indicate that the components of SU Lyn were interacting only for a short time during the last twelve years of monitoring. For the first time, we showed that SU Lyn resembled a classical symbiotic star when it was X-ray bright, and remained hidden afterwards. We also discuss the current evolutionary status of the red giant, as well as possible future evolution of the system. We suggest that SU Lyn could be a progenitor of a classical, persistent symbiotic system.

Hen 3-860: new southern eclipsing symbiotic star observed in the outburst

ABSTRACT Brightening of Hen 3-860, previously classified as an Hα emitter, was detected by the All-Sky Automated Survey for Supernovae (ASAS-SN) survey at the end of the year 2016. We have obtained the first spectroscopic observations of the transient and supplemented them with photometric data from the Digital Access to a Sky Century at Harvard (DASCH) archive of astronomical plates, All-Sky Automated Survey (ASAS), and ASAS-SN surveys. Based on the results of our analysis, we can classify the object as a classical symbiotic star of the infrared type S, consisting of an M2-3 giant with a temperature of Tg ∼ 3550 K, a radius of Rg ∼ 60–75 R⊙, and a luminosity of Lg ∼ 540–760 L⊙, and a hot and luminous component (Th ∼ 1 × 105–2 × 105 K and $L_{\rm h}\, \sim 10^3\, L_\odot$). The system experienced at least four outbursts in the last 120 years. In addition to the outbursts, its light curves revealed the presence of eclipses of the hot component and its surrounding (relatively cool) shell, which developed during the outburst and redistributed a fraction of the radiation of the hot component into the optical, by the giant, classifying the object as a representative of a group of eclipsing symbiotic stars. The eclipses allowed us to reveal the orbital period of the system to be 602 d.

Classical Novae at Radio Wavelengths

Abstract We present radio observations (1–40 GHz) for 36 classical novae, representing data from over five decades compiled from the literature, telescope archives, and our own programs. Our targets display a striking diversity in their optical parameters (e.g., spanning optical fading timescales, t 2 = 1–263 days), and we find a similar diversity in the radio light curves. Using a brightness temperature analysis, we find that radio emission from novae is a mixture of thermal and synchrotron emission, with nonthermal emission observed at earlier times. We identify high brightness temperature emission (T B > 5 × 104 K) as an indication of synchrotron emission in at least nine (25%) of the novae. We find a class of synchrotron-dominated novae with mildly evolved companions, exemplified by V5589 Sgr and V392 Per, that appear to be a bridge between classical novae with dwarf companions and symbiotic binaries with giant companions. Four of the novae in our sample have two distinct radio maxima (the first dominated by synchrotron and the later by thermal emission), and in four cases the early synchrotron peak is temporally coincident with a dramatic dip in the optical light curve, hinting at a common site for particle acceleration and dust formation. We publish the light curves in a machine-readable table and encourage the use of these data by the broader community in multiwavelength studies and modeling efforts.

Optical spectroscopic observations of a symbiotic star MWC 560 in the mass accumulation phase

Abstract There are about a dozen symbiotic stars known to produce high-velocity jets during outbursts. MWC 560 (V694 Mon) is a symbiotic star that seems to show a permanent jet. After showing an unexpected brightening in 2018 November, it has continued to brighten until 2021 and is currently in the brightest state ever. We have been conducting long-term high-dispersion spectroscopic monitoring of this object since 2016 March. An emission wing with vFWHM ≈ 700 km s−1 in the hydrogen Balmer line at an unexpected brightening event in 2018 was reported by Ando et al. (2021, PASJ, 73, L1). In subsequent continuous observations, this emission wing was no longer seen on 2019 February 6. The absorption lines seen in the hydrogen Balmer lines are gradually deepening and spreading to the slower side of the velocity, and the outflow velocity is becoming slower. The expanding component generated by the outburst was initially observed in the emission wing just after the 2018 outburst, got gradually cooler, and was observed in the absorption line after 2019.

Symbiotic Stars in the Apache Point Observatory Galactic Evolution Experiment Survey: The Case of LIN 358 and SMC N73 (LIN 445a)

Abstract LIN 358 and SMC N73 are two symbiotic binaries in the halo of the Small Magellanic Cloud, each composed of a hot white dwarf accreting from a cool giant companion. In this work, we characterize these systems using a combination of spectral energy distribution (SED)-fitting to the extant photometric data spanning a broad wavelength range (X-ray/ultraviolet to near-infrared), detailed analysis of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra for the giant stars, and orbit fitting to high quality radial velocities from the APOGEE database. Using the calculated Roche lobe radius for the giant component and the mass ratio for each system, it is found that LIN 358 is likely undergoing mass transfer via wind Roche lobe overflow, while the accretion mechanism for SMC N73 remains uncertain. This work presents the first orbital characterization for both of these systems (yielding periods of >270 and >980 days, respectively, for SMC N73 and LIN 358) and the first global SED fitting for SMC N73. In addition, variability was identified in APOGEE spectra of LIN 358 spanning 17 epochs over two years that may point to a time variable accretion rate as the product of an eccentric orbit.

Investigating the true nature of three hard X-ray sources

ABSTRACT Many of the new high energy sources discovered both by INTEGRAL/IBIS and Swift/BAT have been characterized thanks to extensive, multiband follow-up campaigns, but there are still objects whose nature remains to be asserted. In this paper, we investigate the true nature of three high energy sources, IGR J12134−6015, IGR J16058−7253, and Swift J2037.2+4151, employing multiwavelength data from the near-infrared to the X-rays. Through Gaia and ESO-VLT measurements and through Swift/XRT X-ray spectral analysis, we re-evaluate the classification for IGR J12134−6015, arguing that the source is a Galactic object and in particular a cataclysmic variable. We were able to confirm, thanks toNuclear Spectroscopic Telescope Array(NuSTAR) observations, that the hard X-ray emission detected by INTEGRAL/IBIS and Swift/BAT from IGR J16058−7253 is coming from two Seyfert 2 galaxies which are both counterparts for this source. Through optical and X-ray spectral analysis of SwiftJ2037.2+4151 we find that this source is likely part of the rare and peculiar class of symbiotic X-ray binaries and displays flux and spectral variability as well as interesting spectral features, such as a blending of several emission lines around the iron line complex.

Optical emission-line spectra of symbiotic binaries

ABSTRACT Symbiotic stars are long-period interacting binaries where the compact object, most commonly a white dwarf, is embedded in the dense stellar wind of an evolved companion star. Ultraviolet and soft X-ray emission of the accretion disc and the nuclear-burning white dwarf plays a major role in shaping the ionization balance of the surrounding wind material, giving rise to the rich line emission. In this paper, we employ two-dimensional photoionization calculations based on the cloudy code to study the ionization state of the circumbinary material in symbiotic systems and to predict their emission-line spectra. Our simulations are parametrized via the orbital parameters of the binary and the wind mass-loss rate of the donor star, while the mass accretion rate, temperature and luminosity of the white dwarf are computed self-consistently. We explore the parameter space of symbiotic binaries and compute luminosities of various astrophysically important emission lines. The line ratios are compared with traditional diagnostic diagrams used to distinguish symbiotic binaries from other types of sources, and it is shown how the binary system parameters shape these diagrams. In the significant part of the parameter space, the wind material is nearly fully ionized, except for the ‘shadow’ behind the donor star, so the white dwarf emission is typically freely escaping the system.

The symbiotic binary ZZ CMi: Intranight variability and suggested outbursting nature

AbstractWe present photometric and spectral observations of the symbiotic star ZZ CMi. We detect intranight variability—flickering and smooth variations in U band. The amplitude of the flickering is about mag in U band. In the B band, the variability is lower, with amplitude mag. We also detect variability in the and emission lines, and find an indication for outflow with velocity of about 120–150 km/s. The results indicate that ZZ CMi is an accretion‐powered symbiotic containing an M4‐M6 III cool component with a white dwarf resembling recurrent novae and jet‐ejecting symbiotic stars.

X-ray observations of two candidate symbiotic binaries in the galactic bulge

ABSTRACT This paper analyses X-ray observations by the Chandra X-ray Observatory of CXOGBS J174614.3−321949 (CXB3) and CXOGBS J173620.2−293338 (CX332), two symbiotic binary star candidates identified by the Galactic Bulge Survey. Using new Chandra observations, we improved their X-ray positional uncertainties to 0.24 and 0.92 arcsec, respectively, confidently associating them with single optical counterparts. In particular, new observations of symbiotic X-ray candidate CX332 further solidify confidence in its coincidence with a carbon star. We demonstrate X-ray variability in both targets with a more recent observation of CX332 showing a decrease in brightness by a factor of 30, while CXB3 observations show it usually in a quiescent state with a factor-of-6 flare-like event in the final observations. In a combined spectral fit for CXB3, we find an NH value of $\sim (2\!-\! 3) \times 10^{22}\, \rm {cm}^{-2}$ with a Γ value of $1.5^{+0.2}_{-0.2}$ for a power-law fit and kT$10.6_{-2.9}^{+5.7}$ keV for an apec fit and an estimated luminosity of ∼8.4 × 1032 erg s−1. Spectra of CXB3 would be consistent with thermal emission as seen in white dwarf symbiotic systems, but the high X-ray luminosity in the light curve is more typically seen in symbiotic X-ray binary systems. Optical spectra of both objects taken with Gemini GMOS indicate CXB3 as containing an M-type star and CX332 having a carbon star counterpart. Both targets show at most marginal evidence of H α emission favouring a symbiotic X-ray binary interpretation for both sources, though we cannot rule out a white dwarf for either case.

Spectroscopic and photometric analysis of symbiotic candidates – I. Ten candidates on classical symbiotic stars

ABSTRACT Symbiotic stars belong to a group of interacting binaries that display a wide variety of phenomena, including prominent outbursts connected with mass transfer, as well as stellar winds, jets, eclipses, or intrinsic variability of the components. Dozens of new symbiotic stars and candidates have been discovered in recent years. However, there are many objects that are still poorly studied. Some symbiotic candidates suspected in the literature have never been studied spectroscopically. In this contribution, we present the first results of the ongoing campaign focused on symbiotic candidates. In the first paper in the series, we study the nature of 10 candidate classical symbiotic stars suspected based on their photometric behaviour, colours or abundance pattern. To confirm or reject the symbiotic nature of the studied candidates, we obtained new spectra and analysed them in detail together with available multifrequency photometric and spectroscopic observations of the objects. Hen 3−860 and V2204 Oph are genuine symbiotic systems showing typical spectral features of burning symbiotic stars and outbursts in the last 100 yr. The first object belongs to the uncommon group of eclipsing symbiotic stars. V1988 Sgr cannot be classified as a genuine burning symbiotic star, but the scenario of an accreting-only symbiotic system cannot be ruled out. Hen 4−204 might be a bonafide symbiotic star due to its similarity with the known symbiotic binary BD Cam. Six other symbiotic candidates (V562 Lyr, IRAS 19050+0001, EC 19249−7343, V1017 Cyg, PN K1−6, V379 Peg) are either single dwarf or giant stars or non-symbiotic binaries.

The GALAH survey and symbiotic stars – I. Discovery and follow-up of 33 candidate accreting-only systems

ABSTRACT We have identified a first group of 33 new candidates for symbiotic stars (SySt) of the accreting-only variety among the 600 255 stars so far observed by the GALactic Archaeology with HERMES (GALAH) high-resolution spectroscopic survey of the Southern hemisphere, more than doubling the number of those previously known. GALAH aims to high latitudes and this offers the possibility to sound the Galaxy for new SySt away from the usual plane and bulge hunting regions. In this paper, we focus on SySt of the M spectral type, showing an Hα emission with a peak in excess of 0.5 above the adjacent continuum level, and not affected by coherent radial pulsations. These constraints will be relaxed in future studies. The 33 new candidate SySt were subjected to an array of follow-up confirmatory observations [X-ray/ultraviolet (UV) observations with the Swift satellite, search for optical flickering, presence of a near-UV upturn in ground-based photometric and spectroscopic data, radial velocity changes suggestive of orbital motion, and variability of the emission-line profiles]. According to Gaia Early Data Release 3 (EDR3) parallaxes, the candidate new SySt are located at the tip of the giant branch, sharing the same distribution in M(Ks) of the well-established SySt. The accretion luminosities of the candidate new SySt are in the range 1–10 L⊙, corresponding to mass accretion rates of 0.1–1 × 10−9 M⊙ yr−1 for white dwarfs of 1 M⊙. The M giant of one of them presents a large lithium overabundance.

Somangnet: Small Telescope Network of Korea

Even in an era where 8-meter class telescopes are common, small telescopes are considered very valuable research facilities since they are available for rapid follow-up or long term monitoring observations. To maximize the usefulness of small telescopes in Korea, we established the SomangNet, a network of 0.4-1.0 m class optical telescopes operated by Korean institutions, in 2020. Here, we give an overview of the project, describing the current participating telescopes, its scientific scope and operation mode, and the prospects for future activities. SomangNet currently includes 10 telescopes that are located in Australia, USA, and Chile as well as in Korea. The operation of many of these telescopes currently relies on operators, and we plan to upgrade them for remote or robotic operation. The latest SomangNet science projects include monitoring and follow-up observational studies of galaxies, supernovae, active galactic nuclei, symbiotic stars, solar system objects, neutrino/gravitational-wave sources, and exoplanets.

Photometry and spectroscopy of the new symbiotic star 2SXPS J173508.4-292958

We present and discuss the results of our photometric and spectroscopic monitoring of 2SXPS J173508.4-292958 carried out from April to August 2020. This X-ray source, in the foreground with respect to the Galactic center, brightened in X-rays during 2020, prompting our follow-up optical observations. We found the star to contain a K4III giant with a modest but highly variable Halpha emission, composed by a ~470 km/s wide component with superimposed a narrow absorption, offset by a positive velocity with respect to the giant. No orbital motion is detected for the K4III, showing an heliocentric radial velocity stable at -12(+/-1) km/s. No flickering in excess of 0.005 mag in B band was observed at three separate visits of 2SXPS J173508.4-292958. While photometrically stable in 2016 through 2018, in 2019 the star developed a limited photometric variability, that in 2020 took the form of a sinusoidal modulation with a period of 38 days and an amplitude of 0.12 mag in V band. We argue this variability cannot be ascribed to Roche-lobe filling by the K4III star. No correlation is observed between the photometric variability and the amount of emission in Halpha, the latter probably originating directly from the accretion disk around the accreting companion. While no emission from dust is detected at mid-IR wavelengths, an excess in U-band is probably present and caused by direct emission from the accretion disk. We conclude that 2SXPS J173508.4-292958 is a new symbiotic star of the accreting-only variety (AO-SySt).

Constraints on the sub-pc environment of the nearby Type Iax SN 2014dt from deep X-ray and radio observations

ABSTRACT We present X-ray and radio observations of what may be the closest Type Iax supernova (SN) to date, SN 2014dt (d = 12.3–19.3 Mpc), and provide tight constraints on the radio and X-ray emission. We infer a specific radio luminosity $L_R\lt (1.0\!-\!2.4)\times 10^{25}\, \rm {erg\, s^{-1}\, Hz^{-1}}$ at a frequency of 7.5 GHz and a X-ray luminosity $L_X\lt 1.4\times 10^{38}\, \rm {erg\, s^{-1}}$ (0.3–10 keV) at ∼38–48 d post-explosion. We interpret these limits in the context of Inverse Compton (IC) emission and synchrotron emission from a population of electrons accelerated at the forward shock of the explosion in a power-law distribution $N_e(\gamma _e)\propto \gamma _e^{-p}$ with p = 3. Our analysis constrains the progenitor system mass-loss rate to be $\dot{M}\lt 5.0 \times 10^{-6} \rm {M_{\odot }\, yr^{-1}}$ at distances $r\lesssim 10^{16}\, \rm {cm}$ for an assumed wind velocity $v_w=100\, \rm {km\, s^{-1}}$, and a fraction of post-shock energy into magnetic fields and relativistic electrons of ϵB = 0.01 and ϵe = 0.1, respectively. This result rules out some of the parameter space of symbiotic giant star companions, and it is consistent with the low mass-loss rates expected from He-star companions. Our calculations also show that the improved sensitivity of the next-generation Very Large Array (ngVLA) is needed to probe the very low-density media characteristic of He stars that are the leading model for binary stellar companions of white dwarfs giving origin to Type Iax SNe.

Radio Spectral Index Analysis of Southern Hemisphere Symbiotic Stars

Abstract Symbiotic stars show emission across the electromagnetic spectrum from a wide array of physical processes. At centimeter waves, both synchrotron and thermal emissions are seen, often highly variable and associated with outbursts in the optical and X-rays. Most models of the radio emission include an ionized region within the dense wind of the red giant star that is kept ionized by activity on the white dwarf companion or its accretion disk. In some cases, there is ongoing shell burning on the white dwarf due to its high mass accretion rate or a prior nova eruption; in other cases, nuclear fusion occurs only occasionally as recurrent nova events. In this study, we measure the spectral indices of a sample of symbiotic systems in the Southern Hemisphere using the Australia Telescope Compact Array. Putting our data together with results from other surveys, we derive the optical depths and brightness temperatures of some well-known symbiotic stars. Using parallax distances from Gaia Data Release 3, we determine the sizes and characteristic electron densities in the radio emission regions. The results show a range of a factor of 104 in radio luminosity and a factor of 100 in linear size. These numbers are consistent with a picture where the rate of shell burning on the white dwarf determines the radio luminosity. Therefore, our findings also suggest that radio luminosity can be used to determine whether a symbiotic star is powered by accretion alone or also by shell burning.