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T. A. Rector

Publications and source records attributed to T. A. Rector.

At least 19 recordsLinked to original sources
arXiv2026

Mapping Active Star-Formation in Serpens and the Aquila Rift

We report the results of a high-sensitivity survey for Herbig-Haro (HH) outflows in the Serpens-Aquila Rift using the DECam instrument on the 4-meter telescope. We have detected 88 new HH objects, more than tripling the total known in this region. We have also identified likely progenitors for most of these outflows. By combining HH object and progenitor locations with literature dust maps and Gaia astrometry, we find that HH objects mark five spatially distinct clouds hosting active star formation: the Serpens Molecular Cloud and LDN 673 at 400-500 pc, the more distant West and East components of the Aquila Rift at ~600 and 700 pc, respectively, and a near cloud in Serpens at ~250 pc. In both the Serpens Molecular Cloud and the Western Aquila Rift, HH objects broadly trace gas structures on the edges of low-density cavities surrounding known stellar populations, consistent with active star formation in feedback-driven shells. The near cloud in Serpens is not associated with any established stellar population, but its position and velocity suggest that it is part of the Local Bubble. And the HH objects there may mark the start of a new stellar generation connected to the Scutum North Association. Our Herbig-Haro objects therefore serve as a powerful indicator of star formation sites even in the absence of astrometrically characterized young stars, making them a useful tool for guiding future YSO surveys.

astro-ph.GA↗
arXiv2026

A Three-Decade VLBI Study of the Nucleus in the Lobe-Dominated Quasar 3C207

We present results from very-long-baseline-interferometry (VLBI) observations of the nucleus in the lobe-dominated quasar 3C207. These observations were completed at 8.4 or 10.7 GHz (X-band) from 1981 to 2010, spanning 29 years. The nucleus of 3C207 is the strongest and most variable in the 3CR complete sample of LDQs, which is under study to test relativistic jet models over a wide range of jet orientation angles. Images have typical resolutions of ~0.5-1.0 milliarcseconds (mas) and sensitivities of ~0.1-0.2 mJy beam^{-1}. The VLBI core region has flux density outbursts at mean intervals of ~7 yr; two of these are multiple outbursts from a stationary "true: core that feeds a "swinging component" ~0.5 mas to the east. The position angle (PA) of the swinging component shows a long-term increase of ~40{\deg}, with a short-term reversal of ~10{\deg}. A one-sided, curved VLBI jet extends ~25 mas eastward, with components spanning a PA range of ~25{\deg}. The jet components have average apparent transverse velocities ~10c. One component shows apparent acceleration from 7c to 14c at 2-3 mas from the true core, where the flow is redirected toward PA ~90{\deg}. Another component shows marginal evidence for apparent deceleration. Individual jet components expand until reaching the recollimation zone. Our results are consistent with a physical model in which 3C207 has quasi-periodic outbursts, jet precession by ballistic components on a conical surface with a small opening angle, and a recollimation process that modifies component motions and narrows the conical geometry on a scale of ~100 pc.

astro-ph.GA↗
arXiv2026

Multi-Sensor Trajectory Reconstruction of the 24 April 2025 Alaska Fireball and Implications for Planetary Defense

On 24 April 2025 at 18:30:57 UTC, a bright daytime fireball over Southcentral Alaska was detected by 37 seismic stations, 16 single infrasound sensors, and four infrasound arrays, yielding 30 ballistic and multiple fragmentation arrivals. The unprecedented density of seismoacoustic coverage enabled detailed reconstruction of the event using acoustic signals, with fragmentation source locations further guiding the identification of Doppler weather radar signatures of a meteorite fall. Incorporation of a radar-derived terminal point yielded a final trajectory solution, which agreed closely with an independent optical trajectory solution from video analysis. The reconstructed entry parameters from seismoacoustic analysis indicate a velocity of 25.3 km/s, an entry angle of 19{\deg}, and an energy release of ~38 t TNT equivalent. Assuming a chondritic composition, the pre-entry object diameter was ~0.7 m. Using orbital parameters from the optical solution, we estimate meteoroid composition as most likely a L-type ordinary chondrite. The event occurred in the sub-Arctic, where space-based optical systems face challenges in detection, demonstrating the critical role of dense ground-based seismoacoustic networks in characterizing highlatitude atmospheric entries. This uniquely well-recorded event demonstrates the capability of dense seismoacoustic networks to constrain bolide trajectories, energetics, and fragmentation, with radar and optical data providing critical confirmation and complementary perspectives. These results bridge the methodological gap between planetary-defense monitoring of natural impactors and space-traffic analyses of artificial reentries, illustrating how multi-sensor integration can deliver calibration-grade trajectories even for unpredicted events.

astro-ph.EP↗
arXiv2025

The Herbig-Haro Outflow Content and Star-Forming Environment of Circinus West and East

We report the results of a spatially compete, high-sensitivity survey for Herbig-Haro (HH) outflows in the Western and Eastern Circinus molecular clouds. We have detected 28 new HH objects in Circinus West, doubling the number known in this dark nebula. We have also discovered 9 outflows in Circinus East, the first to be identified here. Although both Circinus West and East appear to be located at ~800 pc, their morphologies are distinct. Circinus West shows filamentary structure, while Circinus East is dominated by amorphous dark clouds. North-east of Circinus East, an extended distribution of young stars is centered on the ~6 Myr-old open cluster ASCC 79, which may have triggered the sequential formation of younger surrounding populations. New transverse velocities from Gaia show two dynamically distinct stellar populations in Circinus East; their velocity distribution is consistent with an active cloud-cloud collision between material ejected by the formation of O and B stars in ASCC~79 and a dynamically similar interloping cloud. Given the similar distances to Circinus West and East, and the presence in both of HH objects -- a phenomenon associated with stellar ages of ~1 Myr -- it is likely that these clouds are nominally related, but only Circinus East is subject to substantial feedback from the central cluster in the parent complex. This feedback appears to guide the morphology and evolution of Circinus East, resulting in a complex and possibly disruptive dynamical environment rich in star formation potential that contrasts with the relatively quiescent environment in Circinus West.

astro-ph.GA↗
arXiv2024

Climate Change Task Force Report for the American Astronomical Society

The AAS Strategic Plan for 2021-26 called for the creation of a task force to identify how the AAS can meet the goals of the Paris Agreement. The AAS and its membership recognize the danger climate change represents to humanity and our world, and to astronomy -- as a profession, a hobby, and a cultural good. Our profession in general -- and the AAS in particular -- should work to make it possible for all astronomers to have an equal opportunity to be successful without needing to incur high carbon emissions, and to preserve astronomy for future generations. A study was completed of the carbon emissions associated with the AAS, finding that 84% of total AAS-related emissions are from in-person conferences. We also conducted a survey of AAS members to determine their attitudes about climate change. Respondents overwhelmingly (97%) think that the AAS should reduce its carbon footprint. Our task force created a list of fourteen recommendations, with two ranked as top priorities: The AAS should not schedule additional in-person meetings before 2030 and it should work to innovate the AAS conference model. Based upon our analysis it is clear that online interaction is the only way to increase participation while meaningfully decreasing emissions. Our recommendations are aligned with the Astro2020 Decadal Survey as well as AAS values to disseminate our scientific understanding of the universe, and to do our work in an ethically responsible way. Because of their other benefits -- particularly in making our society more welcoming to those who traditionally have been excluded -- we feel that these are sound decisions, worthy of implementation even if the AAS wasn't trying to reduce its carbon footprint. They simply make sense as steps towards a professional society that better serves a broader membership, as our profession evolves to be greener, more inclusive, and more productive.

physics.soc-ph↗
arXiv2017

The Discovery of Herbig-Haro Objects in LDN 673

We report the discovery of twelve faint Herbig-Haro (HH) objects in LDN 673 found using a novel color-composite imaging method that reveals faint Hα emission in complex environments. Follow-up observations in [S II] confirmed their classification as HH objects. Potential driving sources are identified from the Spitzer c2d Legacy Program catalog and other infrared observations. The twelve new HH objects can be divided into three groups: Four are likely associated with a cluster of eight YSO class I/II IR sources that lie between them; five are colinear with the T Tauri multiple star system AS 353, and are likely driven by the same source as HH 32 and HH 332; three are bisected by a very red source that coincides with an infrared dark cloud. We also provide updated coordinates for the three components of HH 332. Inaccurate numbers were given for this object in the discovery paper. The discovery of HH objects and associated driving sources in this region provides new evidence for star formation in the Aquila clouds, implying a much larger T Tauri population in a seldom-studied region.

astro-ph.SR↗
arXiv2014

Recurrent Novae in M31

The reported positions of 964 suspected nova eruptions in M31 recorded through the end of calendar year 2013 have been compared in order to identify recurrent nova candidates. To pass the initial screen and qualify as a recurrent nova candidate two or more eruptions were required to be coincident within 0.1', although this criterion was relaxed to 0.15' for novae discovered on early photographic patrols. A total of 118 eruptions from 51 potential recurrent nova systems satisfied the screening criterion. To determine what fraction of these novae are indeed recurrent the original plates and published images of the relevant eruptions have been carefully compared. This procedure has resulted in the elimination of 27 of the 51 progenitor candidates (61 eruptions) from further consideration as recurrent novae, with another 8 systems (17 eruptions) deemed unlikely to be recurrent. Of the remaining 16 systems, 12 candidates (32 eruptions) were judged to be recurrent novae, with an additional 4 systems (8 eruptions) being possibly recurrent. It is estimated that ~4% of the nova eruptions seen in M31 over the past century are associated with recurrent novae. A Monte Carlo analysis shows that the discovery efficiency for recurrent novae may be as low as 10% that for novae in general, suggesting that as many as one in three nova eruptions observed in M31 arise from progenitor systems having recurrence times <~100 yr. For plausible system parameters, it appears unlikely that recurrent novae can provide a significant channel for the production of Type Ia supernovae.

astro-ph.SR↗
arXiv2008

The Rosette Eye: the key transition phase in the birth of a massive star

Massive protostars dramatically influence their surroundings via accretion-induced outflows and intense radiation fields. They evolve rapidly, the disk and infalling envelope being evaporated and dissipated in $\sim$ 10$^5$ years. Consequently, they are very rare and investigating this important phase of early stellar evolution is extremely difficult. Here we present the discovery of a key transient phase in the emergence of a massive young star, in which ultraviolet radiation from the new-born giant has just punctured through its natal core. The massive young stellar object AFGL 961 II is readily resolved in the near infrared. Its morphology closely resembles a cat's eye and is here dubbed as the Rosette Eye. Emerging ionized flows blow out an hourglass shaped nebula, which, along with the existence of strong near-infrared excess, suggests the existence of an accretion disk in the perpendicular direction. The lobes of the hourglass, however, are capped with arcs of static H$_{2}$ emission produced by fluorescence. This study has strong implications for our understanding of how massive stars embark on their formation.

astro-ph↗
arXiv2008

"Dark Matter" in Accretion Disks

Using Spitzer Space Telescope photometric observations of the eclipsing, interacting binary WZ Sge, we have discovered that the accretion disk is far more complex than previously believed. Our 4.5 and 8 micron time series observations reveal that the well known gaseous accretion disk is surrounded by an asymmetric disk of dusty material with a radius approximately 15 times larger than the gaseous disk. This dust ring contains only a small amount of mass and is completely invisible at optical and near-IR wavelengths, hence consisting of "dark matter". We have produced a model dust ring using 1 micron spherical particles with a density of 3 g/cm$^3$ and with a temperature profile ranging from 700-1500K. Our discovery about the accretion disk structure and the presence of a larger, outer dust ring have great relevance for accretion disks in general, including those in other interacting binary systems, pre-main sequence stars, and active galaxies.

astro-ph↗
arXiv2007

Fast transition between Classical and Weak lined T Tauri stars due to external UV dissipation

The discovery of optical jets immersed in the strong UV radiation field of the Rosette Nebula sheds new light on, but meanwhile poses challenges to, the study of externally irradiated jets. The jet systems in the Rosette are found to have a high state of ionization and show unique features. In this paper, we investigate the evolutionary status of the jet driving sources for young solar-like stars. To our surprise, these jet sources indicate unexpected near infrared properties with no excess emission. They are bathed in harsh external UV radiation such that evaporation leads to a fast dissipation of their circumstellar material. This could represent a transient phase of evolution of young solar-like stars between classical and weak lined T Tauri stars. Naked T Tauri stars formed in this way have indistinguishable evolutionary ages from those of classical T Tauri stars resulting from the same episode of star formation. However, it would be hard for such sources to be identified if they are not driving an irradiated jet in a photoionized medium.

astro-ph↗
arXiv2006

The 2dF BL Lac Survey II

We report on our further analysis of the expanded and revised sample of potential BL Lac objects (the 2BL) optically identified from two catalogues of blue-selected (UV excess) point sources, the 2dF and 6dF QSO Redshift Surveys (2QZ and 6QZ). The 2BL comprises 52 objects with no apparent proper motion, over the magnitude range 16.0 < bj< 20.0. Follow-up high signal-to-noise spectra of 36 2BL objects and NIR imaging of 18 objects, together with data for 19 2BL objects found in the Sloan Digital Sky survey (SDSS), show 17 objects to be stellar, while a further 16 objects have evidence of weak, broad emission features, although for at least one of these the continuum level has clearly varied. Classification of three objects remains uncertain,with NIR results indicating a marked reduction in flux as compared to SDSS optical magnitudes. Seven objects have neither high signal-to-noise spectra nor NIR imaging. Deep radio observations of 26 2BL objects at the VLA resulted in only three further radio-detections, however none of the three is classed as a featureless continuum object. Seven 2BL objects with a radio detection are confirmed as candidate BL Lac objects while one extragalactic (z=0.494) continuum object is undetected at radio frequencies. One further radio-undetected object is also a potential BL Lac candidate. However it would appear that there is no significant population of radio-quiet BL Lac objects.

astro-ph↗
arXiv2005

Faint Radio Sources in the NOAO Bootes Field. VLBA Imaging and Optical Identifications

As a step toward investigating the parsec-scale properties of faint extragalactic radio sources, the Very Long Baseline Array (VLBA) was used at 5.0 GHz to obtain phase-referenced images of 76 sources in the NOAO Bootes field. These 76 sources were selected from the FIRST catalog to have peak flux densities above 10 mJy at 5 arcsec resolution and deconvolved major diameters of less than 3 arcsec at 1.4 GHz. Fifty-seven of these faint radio sources were identified with accretion-powered radio galaxies and quasars brighter than 25.5 mag in the optical I band. On VLA scales at 1.4 GHz, a measure of the compactness of the faint sources (the ratio of the peak flux density from FIRST to the integrated flux density from the NVSS catalog) spans the full range of possibilites arising from source-resolution effects. Thirty of the faint radio sources, or 39 +9/-7%, were detected with the VLBA at 5.0 GHz with peak flux densities above 6 sigma ~2 mJy at 2 mas resolution. The VLBA detections occur through the full range of compactness ratios. The stronger VLBA detections can themselves serve as phase-reference calibrators, boding well for opening up much of the radio sky to VLBA imaging. For the adopted cosmology, the VLBA resolution correponds to 17 pc or finer. Most VLBA detections are unresolved or slightly resolved but one is diffuse and five show either double or core-jet structures; the properties of these latter six are discussed in detail. Three VLBA detections are unidentified and fainter than 25.5 mag in the optical I band; their properties are highlighted because they likely mark optically-obscured active nuclei at high redshift.

astro-ph↗
arXiv2004

Image-Processing Techniques for the Creation of Presentation-Quality Astronomical Images

The quality of modern astronomical data, the power of modern computers and the agility of current image-processing software enable the creation of high-quality images in a purely digital form. The combination of these technological advancements has created a new ability to make color astronomical images. And in many ways it has led to a new philosophy towards how to create them. A practical guide is presented on how to generate astronomical images from research data with powerful image-processing programs. These programs use a layering metaphor that allows for an unlimited number of astronomical datasets to be combined in any desired color scheme, creating an immense parameter space to be explored using an iterative approach. Several examples of image creation are presented. A philosophy is also presented on how to use color and composition to create images that simultaneously highlight scientific detail and are aesthetically appealing. This philosophy is necessary because most datasets do not correspond to the wavelength range of sensitivity of the human eye. The use of visual grammar, defined as the elements which affect the interpretation of an image, can maximize the richness and detail in an image while maintaining scientific accuracy. By properly using visual grammar, one can imply qualities that a two-dimensional image intrinsically cannot show, such as depth, motion and energy. In addition, composition can be used to engage viewers and keep them interested for a longer period of time. The use of these techniques can result in a striking image that will effectively convey the science within the image, to scientists and to the public.

astro-ph↗
arXiv2004

XMM-Newton observations of the BL Lac MS0205.7+3509: a dense, low-metallicity absorber

The high-frequency-peaked BL Lac, MS0205.7+3509 was observed twice with XMM-Newton. Both X-ray spectra are synchrotron-dominated, with mean 0.2--10keV fluxes of 2.80+/-0.01 and 3.34+/-0.02 E-12 erg/cm^2/s. The X-ray spectra are well fit by a power-law with absorption above the Galactic value, however no absorption edges are detected, implying a low metallicity absorber (Z_\sun = 0.04(+0.03)(-0.01)) or an absorber with redshift above one (best-fit z=2.1 for an absorber with solar abundances). In either case the absorbing column density must be ~9E21 cm^-2. A new optical spectrum is presented, with a MgII absorption doublet detected at z=0.351, but no other significant features. The optical spectrum shows little reddening, implying a low dust to gas ratio in the absorber. MS0205.7+3509 must therefore be viewed through a high column density, low-metallicity gas cloud, probably at z=0.351 and associated with the galaxy that has been shown to be within ~2" of the BL Lac.

astro-ph↗
arXiv2003

A Search for Intraday Variability in the Blazar PKS 2005-489

Rapid, multi-color optical monitoring carried out for a multiwavelength campaign during 22-27 August 2000 is presented for the bright and variable BL Lac object PKS 2005-489. Previous multiwavelength monitoring campaigns of PKS 2005-489 have found complex variability behavior both in flux density and in broadband spectrum, with different modes and timescales from days to hours. During this campaign, PKS 2005-489 was observed to be in an unusual state, bright in the optical but faint in the X-ray, just prior to an X-ray flare that began on 2 September 2000. PKS 2005-489 was also observed to have a flatter optical spectrum than prior epochs. A linear increase in optical flux density was observed during the first 5.2 days of the campaign. However, intraday and color variability were not detected. The large discrepancy between the ratio of X-ray to optical flux density observed during this campaign and that observed in prior epochs indicates a lack of long-term correlation between the two wavebands; and it illustrates that simple particle injection events in the jet are insufficient to explain the long-term variability behavior of this object. Twenty-three in-field standard stars are identified for future optical monitoring programs.

astro-ph↗
arXiv2003

The Radio Structure of High-Energy Peaked BL Lacertae Objects

We present VLA and first-epoch VLBA observations that are part of a program to study the parsec-scale radio structure of a sample of fifteen high-energy-peaked BL Lacs (HBLs). The sample was chosen to span the range of logarithmic X-ray to radio flux ratios observed in HBLs. As this is only the first epoch of observations, proper motions of jet components are not yet available; thus we consider only the structure and alignment of the parsec- and kiloparsec-scale jets. Like most low-energy-peaked BL Lacs (LBLs), our HBL sample shows parsec-scale, core-jet morphologies and compact, complex kiloparsec-scale morphologies. Some objects also show evidence for bending of the jet 10-20pc from the core, suggesting interaction of the jet with the surrounding medium. Whereas LBLs show a wide distribution of parsec- to kpc-scale jet misalignment angles, there is weak evidence that the jets in HBLs are more well-aligned, suggesting that HBL jets are either intrinsically straighter or are seen further off-axis than LBL jets.

astro-ph↗
arXiv2003

High-Resolution Radio Imaging of Gravitational Lensing Candidates in the 1 Jansky BL Lac Sample

While BL Lacertae objects are widely believed to be highly beamed, low-luminosity radio galaxies, many radio-selected BL Lacs have extended radio power levels and optical emission lines that are too luminous to be low-luminosity radio galaxies. Also, Stocke & Rector discovered an excess of MgII absorption systems along BL Lac sightlines compared to quasars, suggesting that gravitational lensing may be another means of creating the BL Lac phenomenon in some cases. We present a search for gravitationally-lensed BL Lacs with deep, high-resolution, two-frequency VLA radio maps of seven lensing candidates from the 1 Jansky BL Lac sample. We find that none of these objects are resolved into an Einstein ring like B 0218+357, nor do any show multiple images of the core. All of the lensing candidates that were resolved show a flat-spectrum core and very unusual, steep-spectrum extended morphology that is incompatible with a multiply lensed system. Thus, while these observations do not rule out microlensing, no macrolensing is observed.

astro-ph↗