Second only to initial mass, the rate of wind-driven mass loss determines the final mass of a massive star and the nature of its remnant. Motivated by the need to reconcile observational values and ...theory, we use a recently vetted technique to analyze the mass-loss rates in a sample of OB stars that generate bow shock nebulae. We measure peculiar velocities from new Gaia parallax and proper motion data and their spectral types from new optical and infrared spectroscopy. For our sample of 70 central stars in morphologically selected bow shock nebulae, 67 are OB stars. The median peculiar velocity is 11 km s−1, significantly smaller than classical "runaway star" velocities. Mass-loss rates for these O and early B stars agree with recently lowered theoretical predictions, ranging from 10−7 M yr−1 for mid-O dwarfs to 10−9 M yr−1 for late O dwarfs-a factor of about 2.7 lower than the often-used Vink et al. formulation. Our results provide the first observational mass-loss rates for B0-B3 dwarfs and giants-10−9 to 10−8 M yr−1. We find evidence for an increase in the mass-loss rates below a critical effective temperature, consistent with predictions of the bistability phenomenon in the range Teff = 19,000-27,000 K. The sample exhibits a correlation between modified wind momentum and luminosity, consistent in slope but lower by 0.43 dex in magnitude compared to canonical wind-luminosity relations. We identify a small subset of objects deviating most significantly from theoretical expectations as probable radiation-driven bow wave nebulae by virtue of their low stellar-to-nebular luminosity ratios. For these, the inferred mass-loss rates must be regarded as upper limits.
Abstract
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
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% ± 6% among SBN central stars, consistent with >28% among runaway Galactic O stars. The large multiplicity fraction among runaways implicates very efficient dynamical ejection rather than binary-supernova origins. The median
v
2D
of SBN central stars is
v
2D
= 14.6 km s
−1
, larger than the median
v
2D
= 11.4 km s
−1
for non-bowshock O stars. Central stars of SBNe have a runaway (
v
2D
> 25 km s
−1
) fraction of 24
−
7
+
9
%, consistent with the
22
−
3
+
3
% for control-sample O stars. Most (76%) SBNe central stars are not runaways. Our analysis of alignment (Δ
PA
) between the nebular morphological and
v
2D
kinematic position angles reveals two populations: a highly aligned (
σ
PA
= 25°) population that includes stars with the largest
v
2D
(31% of the sample) and a random (nonaligned) population (69%). SBNe that lie within or near H
ii
regions comprise a larger fraction of this latter component than SBNe in isolated environments, implicating localized ISM flows as a factor shaping their orientations and morphologies. We outline a new conceptual approach to computing the solar local standard of rest motion, yielding
U
⊙
,
V
⊙
,
W
⊙
= 5.5, 7.5,4.5 km s
−1
.
The rate at which massive stars eject mass in stellar winds significantly influences their evolutionary path. Cosmic rates of nucleosynthesis, explosive stellar phenomena, and compact object genesis ...depend on this poorly known facet of stellar evolution. We employ an unexploited observational technique for measuring the mass-loss rates of O and early-B stars. Our approach, which has no adjustable parameters, uses the principle of pressure equilibrium between the stellar wind and the ambient interstellar medium for a high-velocity star generating an infrared bow shock nebula. Results for 20 bow-shock-generating stars show good agreement with two sets of theoretical predictions for O5-O9.5 main-sequence stars, yielding = 1.3 × 10−6 to 2 × 10−9 . Although values derived for this sample are smaller than theoretical expectations by a factor of about two, this discrepancy is greatly reduced compared to canonical mass-loss methods. Bow-shock-derived mass-loss rates are factors of 10 smaller than H -based measurements (uncorrected for clumping) for similar stellar types and are nearly an order of magnitude larger than P4+ and some other diagnostics based on UV absorption lines. Ambient interstellar densities of at least several cm−3 appear to be required for formation of a prominent infrared bow shock nebula. Measurements of for early-B stars are not yet compelling owing to the small number in our sample and the lack of clear theoretical predictions in the regime of lower stellar luminosities. These results may constitute a partial resolution of the extant "weak-wind problem" for late-O stars. The technique shows promise for determining mass-loss rates in the weak-wind regime.
We have started a long-term reverberation mapping (RM) project using the Wyoming Infrared Observatory 2.3 m telescope titled "Monitoring AGNs with Hβ Asymmetry" (MAHA). The motivations of the project ...are to explore the geometry and kinematics of the gas responsible for complex Hβ emission-line profiles, ideally leading to an understanding of the structures and origins of the broad-line region (BLR). Furthermore, such a project provides the opportunity to search for evidence of close binary supermassive black holes. We describe MAHA and report initial results from our first campaign, from 2016 December to 2017 May, highlighting velocity-resolved time lags for four active galactic nuclei (AGNs) with asymmetric Hβ lines. We find that 3C 120, Ark 120, and Mrk 6 display complex features different from the simple signatures expected for pure outflow, inflow, or a Keplerian disk. While three of the objects have been previously reverberation mapped, including velocity-resolved time lags in the cases of 3C 120 and Mrk 6, we report a time lag and corresponding black hole mass measurement for SBS 1518+593 for the first time. Furthermore, SBS 1518+593, the least asymmetric of the four, does show velocity-resolved time lags characteristic of a Keplerian disk or virialized motion more generally. Also, the velocity-resolved time lags of 3C 120 have significantly changed since previously observed, indicating an evolution of its BLR structure. Future analyses of the data for these objects and others in MAHA will explore the full diversity of Hβ lines and the physics of AGN BLRs.
ABSTRACT We identify 709 arc-shaped mid-infrared nebula in 24 μm Spitzer Space Telescope or 22 μm Wide Field Infrared Explorer surveys of the Galactic Plane as probable dusty interstellar bowshocks ...powered by early-type stars. About 20% are visible at 8 μm or at shorter mid-infrared wavelengths. The vast majority (660) have no previous identification in the literature. These extended infrared sources are strongly concentrated near the Galactic mid-plane, with an angular scale height of ∼0 6. All host a symmetrically placed star implicated as the source of a stellar wind sweeping up interstellar material. These are candidate "runaway" stars potentially having high velocities in the reference frame of the local medium. Among the 286 objects with measured proper motions, we find an unambiguous excess with velocity vectors aligned with the infrared morphology-kinematic evidence that many of these are "runaway" stars with large peculiar motions responsible for the bowshock signature. We discuss a population of "in situ" bowshocks (∼103 objects) that face giant H ii regions where the relative motions between the star and ISM may be caused by bulk outflows from an overpressured bubble. We also identify ∼58 objects that face 8 μm bright-rimmed clouds and apparently constitute a sub-class of in situ bowshocks where the stellar wind interacts with a photoevaporative flow (PEF) from an eroding molecular cloud interface (i.e., "PEF bowshocks"). Orientations of the arcuate nebulae exhibit a correlation over small angular scales, indicating that external influences such as H ii regions are responsible for producing some bowshock nebulae. However, the vast majority of the nebulae in this sample appear to be isolated (499 objects) from obvious external influences.
Arcuate infrared nebulae are ubiquitous throughout the Galactic Plane and are candidates for partial shells, bubbles, or bowshocks produced by massive runaway stars. We tabulate infrared photometry ...for 709 such objects using images from the Spitzer Space Telescope, the Wide-field Infrared Explorer, and the Herschel Space Observatory (HSO). Of the 709 objects identified at 24 or 22 m, 422 are detected at the HSO 70 m bandpass. Of these, only 39 are detected at HSO 160 m. The 70 m peak surface brightnesses are 0.5-2.5 Jy arcmin−2. Color temperatures calculated from the 24 to 70 m ratios range from 80 to 400 K. Color temperatures from 70 to 160 m ratios are systematically lower, 40-200 K. Both of these temperature are, on average, 75% higher than the nominal temperatures derived by assuming that dust is in steady-state radiative equilibrium. This may be evidence of stellar wind bowshocks sweeping up and heating-possibly fragmenting but not destroying-interstellar dust. Infrared luminosity correlates with standoff distance, R0, as predicted by published hydrodynamical models. Infrared spectral energy distributions are consistent with interstellar dust exposed to either single radiant energy density, (in more than half of the objects) or a range of radiant energy densities Umin = 25 to Umax = 103-105 times the mean interstellar value for the remainder. Hence, the central OB stars dominate the energetics, making these enticing laboratories for testing dust models in constrained radiation environments. The spectral energy densities are consistent with polycyclic aromatic hydrocarbon fractions in most objects.
We report the results of reverberation mapping of three bright Seyfert galaxies, Mrk 79, NGC 3227, and Mrk 841, from a campaign conducted from 2016 December to 2017 May with the Wyoming Infrared ...Observatory (WIRO) 2.3 m telescope. All three of these targets have shown asymmetric broad Hβ emission lines in the past, although their emission lines were relatively symmetric during our observations. We measured Hβ time lags for all three targets and estimated masses of their black holes-for the first time in the case of Mrk 841. For Mrk 79 and NGC 3227, the data are of sufficient quality to resolve distinct time lags as a function of velocity and to compute two-dimensional velocity-delay maps. Mrk 79 shows smaller time lags for high-velocity gas, but the distribution is not symmetric, and its complex velocity-delay map could result from the combination of both inflowing and outflowing Hβ emitting disks that may be part of a single larger structure. NGC 3227 shows the largest time lags for blueshifted gas, and the two-dimensional velocity-delay map suggests a disk with some inflow. We compare our results with previous work and find evidence for different time lags despite similar luminosities, as well as evolving broad-line region structures.
Abstract We report first-time reverberation-mapping results for 14 active galactic nuclei (AGNs) from the ongoing Monitoring AGNs with H β Asymmetry campaign (MAHA). These results utilize optical ...spectra obtained with the Long Slit Spectrograph on the Wyoming Infrared 2.3 m Telescope between 2017 November and 2023 May. MAHA combines long-duration monitoring with high cadence. We report results from multiple observing seasons for nine of the 14 objects. These results include H β time lags, supermassive black hole masses, and velocity-resolved time lags. The velocity-resolved lags allow us to investigate the kinematics of the broad-line region.
Arcuate mid-infrared nebulae known as stellar bow shock nebulae (SBNe) have been previously hypothesized to be supported by the strong stellar winds and/or luminosity of massive early-type stars. We ...present an optical spectroscopic survey of 84 stars identified from mid-infrared images as candidate SBN-supporting stars. Eighty-one of 84 sources, 96%, are O or early-B spectral types. K-band luminosities for a larger sample of 289 stars at the centers of bow shock nebulae are overwhelmingly consistent with OB stars. This affirms both that SBNe are supported by massive stars and that arcuate mid-infrared nebulae are reliable indicators of the presence of a massive star. The radial velocity dispersions of these systems and detections of double-lined systems indicate that at least 27 of the 74 systems with multiple observations (>36%) are candidate multiple-star systems. This rate is consistent with observed multiplicity rates of field OB stars detected with similar radial velocity surveys and lower than, but not inconsistent with, the multiplicity rates of OB stars in clusters and associations.
To describe the use of intraluminal tracheal stenting in 3 cats with either benign or malignant tracheal obstruction. Retrospective clinical study. Three client-owned cats. Medical records were ...reviewed and information regarding signalment, clinical signs, physical examination findings, diagnostic tests performed, treatment, outcome and follow-up were retrieved. Intraluminal tracheal stent placement was performed as previously described in the literature. Three cats received intraluminal tracheal stents for the treatment of tracheal obstruction due to 3 different underlying causes: stricture secondary to traumatic endotracheal intubation, stricture secondary to a previous tracheotomy, and neoplasia. Self-expanding metallic stents of varying sizes were placed, and all cats recovered uneventfully from the procedures. The cat with tracheal neoplasia was euthanized because of pulmonary metastatic disease 6 weeks post-stent placement. The two cats with tracheal obstructions secondary to benign strictures are currently 39 months and 32 weeks post-stent placement, respectively. No complications were noted during the post-stent period in any of the 3 cats. Intraluminal tracheal stenting was easily, safely, and rapidly performed without complications and resulted in immediate improvement in clinical signs in all three cases. None of the cats in this study developed significant stent-associated complications during the study period. Intraluminal tracheal stenting has the potential to be a viable option for the treatment of tracheal obstruction in cats and perhaps for similar disease processes in other veterinary patients.
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