Very few examples are known of red supergiant runaways, all of them descending from the more massive O-type precursors, but none from the lower mass B-type precursors, although runaway statistics among B-type stars suggest that K-type runaways must be relatively numerous. We study HD 137071, a star that has been considered so far as a normal K-type red giant. Its parallax measured by Gaia and the derived luminosity suggest that it is actually a supergiant, whereas its derived distance to the galactic plane and its spatial velocity of 54.1 km s$^{-1}$ with respect to the local standard of rest suggest that it is also a runaway star. However, intrinsic limitations in determining the trigonometric parallaxes of cool supergiants, even in the Gaia era, require accurate spectral classifications for confirmation. We reliably classify HD 137071 as a K4II star establishing its membership to the extreme Population I, which is in agreement with the luminosity derived using the Gaia DR2 parallax measurement. Kinematical data from the Gaia DR2 catalog confirm its high spatial velocity and its runaway nature. Combining the spectral classification with astrometric information, a state-of-the-art galactic potential model, and evolutionary models for high-mass stars we trace the motion of HD 137071 back to the proximities of the galactic plane and speculate on which of the two proposed mechanisms for the production of runaway stars may be responsible for the high velocity of HD 137071. The available data favor the formation of HD 137071 in a massive binary system where the more massive companion underwent a supernova explosion about 32 Myr ago.
A significant fraction of massive stars are moving supersonically through the interstellar medium (ISM), either due to disruption of a binary system or ejection from their parent star cluster. The interaction of their wind with the ISM produces a bow shock. In late evolutionary stages these stars may undergo rapid transitions from red to blue and vice versa on the Hertzsprung-Russell diagram, with accompanying rapid changes to their stellar winds and bow shocks. Recent 3D simulations of the bow shock produced by the nearby runaway red supergiant (RSG) Betelgeuse, under the assumption of a cons…
A significant percentage of OB stars are runaways, so we should expect a similar percentage of their evolved descendants to also be runaways. However, recognizing such stars presents its own set of challenges, as these older, more evolved stars will have drifted further from their birthplace, and thus their velocities might not be obviously peculiar. Several Galactic red supergiants (RSGs) have been described as likely runaways, based upon the existence of bow shocks, including Betelgeuse. Here we announce the discovery of a runaway RSG in M31, based upon a 300 km s$^{-1}$ discrepancy with M31…
We search for runaway stars in the Large Magellanic Cloud (LMC) by computing the space velocities of the visually brightest stars in the LMC that are included in the Gaia TGAS proper motion catalog. We compare with predictions from stellar dynamical models to obtain (peculiar) velocities relative to their local stellar environment. Two of the 31 stars have unusually high proper motions. Of the remaining 29 stars we find that most objects in this sample have velocities in very good agreement with model predictions of a circularly rotating disk model. Indeed the excellent fit to the model implie…
We recently discovered a yellow supergiant (YSG) in the Small Magellanic Cloud (SMC) with a heliocentric radial velocity of ~300 km/s which is much larger than expected for a star in its location in the SMC. This is the first runaway YSG ever discovered and only the second evolved runaway star discovered in a different galaxy than the Milky Way. We classify the star as G5-8I, and use de-reddened broad-band colors with model atmospheres to determine an effective temperature of 4700+/-250K, consistent with what is expected from its spectral type. The star's luminosity is then L/Lo ~ 4.2+/-0.1, c…
CONTEXT.The first Gaia Data Release (DR1) significantly improved the previously available proper motions for the majority of the Tycho-2 stars. AIMS. We want to detect runaway stars using Gaia DR1 proper motions and compare our results with previous searches. METHODS. Runaway O stars and BA supergiants are detected using a 2-D proper-motion method. The sample is selected using Simbad, spectra from our GOSSS project, literature spectral types, and photometry processed using CHORIZOS. RESULTS. We detect 76 runaway stars, 17 (possibly 19) of them with no prior identification as such, with an esti…
We report the results of optical spectroscopy of a candidate evolved massive star in the Cygnus X region, TYC 3159-6-1, revealed via detection of its curious circumstellar nebula in archival data of the Spitzer Space Telecope. We classify TYC 3159-6-1 as an O9.5-O9.7 Ib star and derive its fundamental parameters by using the stellar atmosphere code FASTWIND. The He and CNO abundances in the photosphere of TYC 3159-6-1 are consistent with the solar abundances, suggesting that the star only recently evolved off the main sequence. Proper motion and radial velocity measurements for TYC 3159-6-1 sh…
The scope of this paper is to perform a detailed spectroscopic study of the northern O-type supergiant HD 195592. We use a large sample of high quality spectra in order to investigate its multiplicity, and to probe the line profile variability. Our analysis reveals a clear spectroscopic binary signature in the profile of the He {\sc i} $λ$ 6678 line, pointing to a probable O + B system. We report on low amplitude radial velocity variations in every strong absorption line in the blue spectrum of HD 195592. These variations are ruled by two time-scales respectively of 5.063 and about 20 days. Th…
The Perseus OB1 association hosts one of the most populous groupings of blue and red supergiants (Sgs) in the Galaxy. We discuss whether the massive O-type and blue/red Sg stars located in the Per OB1 region are members of the same population and examine their binary and runaway status. We gathered a total of 405 high-resolution spectra for 88 suitable candidates around 4.5 deg from the center of the association, and compiled Gaia DR2 astrometry for all of them. This was used to investigate membership and identify runaway stars. By obtaining high-precision radial velocity (RV) estimates, we in…
Runaway stars ejected from the Galactic disk populate the halo of the Milky Way. To predict the spatial and kinematic properties of runaways, we inject stars into a Galactic potential, compute their trajectories through the Galaxy, and derive simulated catalogs for comparison with observations. Runaways have a flattened spatial distribution, with higher velocity stars at Galactic latitudes less than 30 degrees. Due to their shorter stellar lifetimes, massive runaway stars are more concentrated towards the disk than low mass runaways. Bound (unbound) runaways that reach the halo probably origin…
Runaway stars are stars observed to have large peculiar velocities. Two mechanisms are thought to contribute to the ejection of runaway stars, both involve binarity (or higher multiplicity). In the binary supernova scenario a runaway star receives its velocity when its binary massive companion explodes as a supernova (SN). In the alternative dynamical ejection scenario, runaway stars are formed through gravitational interactions between stars and binaries in dense, compact clusters or cluster cores. Here we study the ejection scenario. We make use of extensive N-body simulations of massive clu…
We explore the hypothesis that B type emission-line stars (Be stars) have their origin in mass-transfer binaries by measuring the fraction of runaway Be stars. We assemble the largest-to-date catalogue of 632 Be stars with 6D kinematics, exploiting the precise astrometry of the Tycho-Gaia Astrometric Solution (TGAS) from the first Gaia Data Release. Using binary stellar evolution simulations, we make predictions for the runaway and equatorial rotation velocities of a runaway Be star population. Accounting for observational biases, we calculate that if all classical Be stars originated through …
Runaway stars can result from core-collapse supernovae in multiple stellar systems. If the supernova disrupts the system, the companion gets ejected with its former orbital velocity. A clear identification of a runaway star can yield the time and place of the explosion as well as orbital parameters of the pre-supernova binary system. Previous searches have mostly considered O- and B-type stars as runaway stars because they are always young in absolute terms (not much older than the lifetime of the progenitor) and can be detected up to larger distances. We present here a search for runaway star…
We predict the distinctive three dimensional space motions of hypervelocity stars (HVSs) and runaway stars moving in a realistic Galactic potential. For nearby stars with distances less than 10~kpc, unbound stars are rare; proper motions alone rarely isolate bound HVSs and runaways from indigenous halo stars. At large distances of 20-100 kpc, unbound HVSs are much more common than runaways; radial velocities easily distinguish both from indigenous halo stars. Comparisons of the predictions with existing observations are encouraging. Although the models fail to match observations of solar-type …
We have detected 13 new runaway-star candidates of spectral type O combining the TGAS (Tycho-Gaia Astrometric Solution) proper motions from Gaia Data Release 1 (DR1) and the sample from GOSSS (Galactic O-Star Spectroscopic Survey). We have also combined TGAS and Hipparcos proper motions to check that our technique recovers many of the previously known O-type runaways in the sample.
Runaway stars are ejected from their place of birth in the Galactic disk, with some young B-type runaways found several tens of kiloparsecs from the plane traveling at speeds beyond the escape velocity. Young open clusters are a likely place of origin, and ejection may be either through N-body interactions or in binary supernova explosions. The excellent quality of Gaia astrometry opens up the path to study the kinematics of young runaway stars to such a high precision that the place of origin in open stellar clusters can be identified uniquely. We developed an efficient minimization method to…
Betelgeuse, a nearby red supergiant, is a runaway star with a powerful stellar wind that drives a bow shock into its surroundings. This picture has been challenged by the discovery of a dense and almost static shell that is three times closer to the star than the bow shock and has been decelerated by some external force. The two physically distinct structures cannot both be formed by the hydrodynamic interaction of the wind with the interstellar medium. Here we report that a model in which Betelgeuse's wind is photoionized by radiation from external sources can explain the static shell without…
Theory predicts that we should find fast, ejected (runaway) stars of all masses around dense, young star-forming regions. $N$-body simulations show that the number and distribution of these ejected stars could be used to constrain the initial spatial and kinematic substructure of the regions. We search for runaway and slower walkaway stars within 100 pc of the Orion Nebula Cluster (ONC) using $Gaia$ DR2 astrometry and photometry. We compare our findings to predictions for the number and velocity distributions of runaway stars from simulations that we run for 4 Myr with initial conditions tailo…
We conduct a theoretical study on the ejection of runaway massive stars from R136 --- the central massive, star-burst cluster in the 30 Doradus complex of the Large Magellanic Cloud. Specifically, we investigate the possibility of the very massive star (VMS) VFTS 682 being a runaway member of R136. Recent observations of the above VMS, by virtue of its isolated location and its moderate peculiar motion, have raised the fundamental question whether isolated massive star formation is indeed possible. We perform the first realistic N-body computations of fully mass-segregated R136-type star clust…
We present the discovery of three new B[e] supergiants (sgB[e] stars) in the Small Magellanic Cloud (SMC). All three stars (R15, R38, and R48) were identified in the course of our Runaways and Isolated O Type Star Spectroscopic Survey of the SMC (RIOTS4). The stars show optical spectra that closely resemble those of previously known B[e] stars, presenting numerous low-ionization forbidden and permitted emission lines such as [Fe II] and Fe II. Furthermore, our stars have luminosities of log(L/L_sun) > 4, demonstrating that they are supergiants. However, we find lower infrared excesses and weak…
Keele University（基尔大学）；Universidad de Alicante（阿利坎特大学）；Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université（巴黎天文台，巴黎文理研究大学，索邦大学，巴黎西岱大学，塞吉-蓬图瓦兹大学）
Two main scenarios have been proposed for origin of massive runaway stars -- dynamical ejection or release from a binary at the first core collapse -- but their relative contribution remains debated. Using two large spectroscopic campaigns towards massive stars in 30 Doradus, we aim to provide observational constraints on the properties of the O-type runaway population in the most massive active star-forming region in the Local group. We use RV measurements of the O-type star populations in 30 Doradus obtained by the VLT-FLAMES Tarantula Survey and the Tarantula Massive Binary Monitoring to id…
We use the Binary Population and Spectral Synthesis (BPASS) models to test the recent suggestion that red supergiants can provide an accurate age estimate of a co-eval stellar population that is unaffected by interacting binary stars. Ages are estimated by using both the minimum luminosity red supergiant and the mean luminosity of red supergiants in a cluster. We test these methods on a number of observed star clusters and find our results in agreement with previous estimates. Importantly we find the difference between the ages derived from stellar population models with and without a realisti…
We discuss the origin of the runaway early B-type star HD271791 and show that its extremely high velocity (\simeq 530-920 km/s) cannot be explained within the framework of the binary-supernova ejection scenario. Instead, we suggest that HD271791 attained its peculiar velocity in the course of a strong dynamical encounter between two hard massive binaries or via an exchange encounter between a hard massive binary and a very massive star, formed through runaway mergers of ordinary massive stars in the dense core of a young massive star cluster.
There are two accepted mechanisms to explain the origin of runaway OB-type stars: the Binary Supernova Scenario (BSS), and the Cluster Ejection Scenario (CES). In the former, a supernova explosion within a close binary ejects the secondary star, while in the latter close multi-body interactions in a dense cluster cause one or more of the stars to be ejected from the region at high velocity. Both mechanisms have the potential to affect the surface composition of the runaway star. TLUSTY non-LTE model atmosphere calculations have been used to determine atmospheric parameters and carbon, nitrogen…
A significant fraction of massive stars move at speed through the interstellar medium of galaxies. After their death as core collapse supernovae, a possible final evolutionary state is that of a fast rotating magnetised neutron star, shaping its circumstellar medium into a pulsar wind nebula. Understanding the properties of pulsar wind nebulae requires knowledge of the evolutionary history of their massive progenitors. Using 2.5D magnetohydrodynamical simulations, we demonstrate that, in the context of a runaway high mass red supergiant supernova progenitor, the morphology of its subsequent pu…
Most runaway OB stars, like the majority of massive stars residing in their parent clusters, go through the red supergiant (RSG) phase during their lifetimes. Nonetheless, although many dozens of massive runaways were found to be associated with bow shocks, only two RSG bow-shock-producing stars, Betelgeuse and μCep, are known to date. In this paper, we report the discovery of an arc-like nebula around the late M-type star IRC-10414 using the SuperCOSMOS H-alpha Survey. Our spectroscopic follow-up of IRC-10414 with the Southern African Large Telescope (SALT) showed that it is a M7 supergiant, …
Wolf-Rayet stars are advanced evolutionary stages of massive stars. Despite their large mass-loss rates and high wind velocities, none of them display a bow shock, although a fraction of them are classified as runaway. Our 2.5-D numerical simulations of circumstellar matter around a 60Mo runaway star show that the fast Wolf-Rayet stellar wind is released into a wind-blown cavity filled with various shocks and discontinuities generated throughout the precedent evolutionary phases. The resulting fast-wind slow-wind interaction leads to the formation of spherical shells of swept-up dusty material…
We explore the possibility that the observed population of Galactic hypervelocity stars (HVSs) originate as runaway stars from the Large Magellanic Cloud (LMC). Pairing a binary evolution code with an N-body simulation of the interaction of the LMC with the Milky Way, we predict the spatial distribution and kinematics of an LMC runaway population. We find that runaway stars from the LMC can contribute Galactic HVSs at a rate of $3 \times 10^{-6}\;\mathrm{yr}^{-1}$. This is composed of stars at different points of stellar evolution, ranging from the main-sequence to those at the tip of the asym…
A significative fraction of all massive stars in the Milky Way move supersonically through their local interstellar medium (ISM), producing bow shock nebulae by wind-ISM interaction. The stability of these observed astrospheres around cool massive stars challenges precedent two-dimensional (magneto-)hydrodynamical simulations of their surroundings. We present three-dimensional magneto-hydrodynamical (3D MHD) simulations of the circumstellar medium of runaway M-type red supergiant stars moving with velocity v_star= 50 km/s. We treat the stellar wind with a Parker spiral and assume a 7 microG ma…
Runaway OB stars are ejected from their parent clusters via two mechanisms, both involving multiple stars: the dynamical ejection scenario (DES) and the binary supernova scenario (BSS). We constrain the relative contributions from these two ejection mechanisms in the Small Magellanic Cloud (SMC) using data for 304 field OB stars from the spatially complete, Runaways and Isolated O-Type Star Spectroscopic Survey of the SMC (RIOTS4). We obtain stellar masses and projected rotational velocities $v_r\sin i $ for the sample using RIOTS4 spectra, and use transverse velocities $v_{\rm loc}$ from $\it…
Young nearby runaway stars are suitable to search for their place of origin and possibly associated objects, for example neutron stars. Tetzlaff, Neuhäuser & Hohle (2011) selected young ($\le 50$ Myr) runaway star candidates from Hipparcos, for which they had estimated the ages from the location in the Hertzsprung-Russell diagram and evolutionary models. Here, we redetermine or constrain their young ages more precisely not only by using the new Gaia DR2 data, but also by measuring lithium, which is a youth indicator. For 308 stars, we took spectra to search for the strong resonance doublet of …
We present evidence that the nebular cocoon and bow-shock emission nebula putatively and recently reported as deriving from the 9th magnitude "runaway" star HD 185806 is the previously discovered but obscure planetary nebula WHTZ 1 (Ra 7). It has a Gaia DR3 G~16 blue ionizing star at its geometric centre. We present imagery, spectroscopy, other data and arguments to support that this emission source is a high excitation Planetary Nebula not a stellar wind bow shock.
Recent supernova and transient surveys have revealed an increasing number of non-terminal stellar eruptions. Though the progenitor class of these eruptions includes the most luminous stars, little is known of the pre-supernova mechanics of massive stars in their most evolved state, thus motivating a census of possible progenitors. From surveys of evolved and unstable luminous star populations in nearby galaxies, we select a sample of yellow and red supergiant candidates in M31 and M33 for review of their spectral characteristics and spectral energy distributions. Since the position of intermed…
In this paper, we study the 3-body products (two single stars and a binary) of binary-binary (2+2) scattering interactions. This is done using a combination of analytic methods and numerical simulations of 2+2 scattering interactions, both in isolation and in a homogeneous background potential. We derive analytically a simple formula relating the angle between the velocity vectors of the two ejected single stars and the orbital separation of the remaining binary. We compare our analytic formulation to numerical scattering simulations, and illustrate that the agreement is excellent, both in iso…
We study the formation of runaway stars due to binary-binary (2+2) interactions in young star-forming clusters and/or associations. This is done using a combination of analytic methods and numerical simulations of 2+2 scattering interactions, both in isolation and in a homogeneous background potential. We focus on interactions that produce two single stars and a binary, and study the outcomes as a function of the depth of the background potential, within a range typical of cluster cores. As reference parameters for the observational properties, we use those observed for the system of runaway s…
OB stars powering stellar bowshock nebulae (SBNe) have been presumed to have large peculiar velocities. We measured peculiar velocities of SBN central stars to assess their kinematics relative to the general O star population using $Gaia$ EDR3 data for 267 SBN central stars and a sample of 455 Galactic O stars to derive projected velocities $v_{\rm 2D}$. For a subset of each sample we obtained new optical spectroscopy to measure radial velocities and identify multiple-star systems. We find a minimum multiplicity fraction of 36$\pm$6% among SBN central stars, consistent with $>$28% among runawa…
Since the discovery of hypervelocity stars in 2005, it has been widely believed that only the disruption of a binary system by a supermassive black hole at the Galactic center (GC), that is, the so-called Hills mechanism, is capable of accelerating stars to beyond the Galactic escape velocity. In the meantime, however, driven by the Gaia space mission, there is mounting evidence that many of the most extreme high-velocity early-type stars at high Galactic latitudes do originate in the Galactic disk and not in the GC. Moreover, the ejection velocities of these extreme disk-runaway stars exceed …
Fast, ejected stars have been found around several young star-forming regions, such as the Orion Nebula Cluster (ONC). These ejected stars can be used to constrain the initial density, spatial and kinematic substructure when compared to predictions from $N$-body simulations. We search for runaway and slower walkaway stars using $Gaia$ DR2 within 100 pc of NGC 2264, which contains subclustered regions around higher-mass OB-stars (S Mon, IRS 1 and IRS 2). We find five runaways and nine walkaways that trace back to S Mon and six runaways and five walkaways that trace back to IRS 1/2 based on thei…
Anomalous surface abundances are observed in a fraction of the low-mass stars of Galactic globular clusters, that may originate from hot-hydrogen-burning products ejected by a previous generation of massive stars. We present and investigate a scenario in which the second generation of polluted low-mass stars can form in shells around cool supergiant stars within a young globular cluster. Simulations of low-Z massive stars (M$_{\rm i}\sim$ 150$-$600 M$_{\odot}$) show that both core-hydrogen-burning cool supergiants and hot ionizing stellar sources are expected to be present simulaneously in you…
We analyzed high angular resolution 45.5 GHz images of the W49 North massive star forming region obtained in 1998 and 2016 with the Very Large Array. Most of the ultracompact HII regions show no detectable changes over the time interval of the observations. However, subcomponents B1, B2, G2a and G2c have increased its peak flux densities by values in the range of 3.8 to 21.4 \%. Most interestingly, the cometary region C clearly shows proper motions that at the distance of the region are equivalent to a velocity of 76$\pm$6 km s$^{-1}$ in the plane of the sky. We interpret this region as the io…
Anticipating the kinematic constraints from the Gaia mission, we perform an extensive numerical study of the evolution of massive binary systems to predict the peculiar velocities that stars obtain when their companion collapses and disrupts the system. Our aim is to (1) identify which predictions are robust against model uncertainties and assess their implications, (2) investigate which physical processes leave a clear imprint and may therefore be constrained observationally and (3) provide a suite of publicly available model predictions. We find that $22_{-8}^{+26}$% of all massive binary sy…
Clear identifications of Galactic young stellar clusters farther than a few kpc from the Sun are rare, despite the large number of candidate clusters. We aim to improve the selection of candidate clusters rich in massive stars with a multiwavelength analysis of photometric Galactic data that range from optical to mid-infrared wavelengths. We present a photometric and spectroscopic analysis of five candidate stellar clusters, which were selected as overdensities with bright stars (Ks < 7 mag) in GLIMPSE and 2MASS images. A total of 48 infrared spectra were obtained. The combination of photometr…
Young massive stars in the halo are assumed to be runaway stars from the Galactic disk. Possible ejection scenarios are binary supernova ejections (BSE) or dynamical ejections from star clusters (DE). Hypervelocity stars (HVSs) are extreme runaway stars that are potentially unbound from the Galaxy. Powerful acceleration mechanisms such as the tidal disruption of a binary system by a supermassive black hole (SMBH) are required to produce them. Therefore, HVSs are believed to originate in the Galactic center (GC), the only place known to host an SMBH. The second Gaia data release (DR2) offers th…
How very massive stars form is still an open question in astrophysics. VFTS682 is among the most massive stars known, with an inferred initial mass of $\sim$150 $M_\odot$ . It is located in 30 Doradus at a projected distance of 29 pc from the central cluster R136. Its apparent isolation led to two hypotheses: either it formed in relative isolation or it was ejected dynamically from the cluster. We investigate the kinematics of VFTS682 as obtained by Gaia and Hubble Space Telescope astrometry. We derive a projected velocity relative to the cluster of $38 \pm 17 \mathrm{km \ s^{-1}}$ (1$σ$ confi…
Hypervelocity stars are rare objects, mostly main-sequence (MS) B stars, traveling so fast that they will eventually escape from the Milky Way. Recently, it has been shown that the popular Hills mechanism, in which a binary system is disrupted via a close encounter with the supermassive black hole at the Galactic center, may not be their only ejection mechanism. The analyses of Gaia data ruled out a Galactic center origin for some of them, and instead indicated that they are extreme disk runaway stars ejected at velocities exceeding the predicted limits of classical scenarios (dynamical ejecti…
We examine the recent star formation associated with four supergiant shells (SGSs) in the Large Magellanic Cloud (LMC): LMC 1, 4, 5, and 6, which have been shown to have simple expanding-shell structures. H II regions and OB associations are used to infer star formation in the last few Myr, while massive young stellar objects (YSOs) reveal the current ongoing star formation. Distributions of ionized, H I, and molecular components of the interstellar gas are compared with the sites of recent and current star formation to determine whether triggering has taken place. We find that a great majorit…
Massive stars becoming red supergiants lose a significant amount of their mass during that brief evolutionary phase. They then either explode as a hydrogen-rich supernova (SN Type II), or continue to evolve as a hotter supergiant (before exploding). The slow, dusty ejecta of the red supergiant will be over-run by the hot star wind and/or SN ejecta. I will present estimates of the conditions for this interaction and discuss some of the implications.
