arXiv subjects

Brian Skiff

Publications and source records attributed to Brian Skiff.

At least 19 recordsLinked to original sources

arXiv2026

NEO Colors from The Mission Accessible Near-Earth Object Survey (MANOS)

We present spectro-photometric griz colors for 189 near-Earth objects (NEOs) collected by the Mission Accessible Near-Earth Object Survey (MANOS). Data acquisition involved non-simultaneous multi-band exposures, thus particular attention was given to the influence of rotational lightcurves on the derived colors. We show that colors measured without accounting for lightcurve variations can significantly influence results for individual objects and potentially have systematic offsets for ensemble studies. Color-based taxonomic classifications were used to investigate the distribution of spectral types. Our results were combined with other visible wavelength surveys to highlight a previously reported change in the observed taxonomic distribution of NEOs as a function of size, namely a decrease in S complex and an increase in X complex objects with increasing absolute magnitude. Plausibility arguments are given to suggest that Main Belt source region, thermal modification, discovery bias, tidal resurfacing, regolith grain size, and impact shock darkening are unlikely explanations for this size-dependent trend. Consistent with recent NEO population models and work on the connection between meteorites and young asteroid families in the Main Belt, this trend is best explained by a compositional gradient in the NEO population. In particular, the observed abundance of S complex or ordinary chondrite-like NEOs decreases by a factor of two from ~65% of the population at km-scales down to a third at sizes <50m. This result has implications for understanding the initial pre-impact population of meteorite parent bodies prior to atmospheric filtering. Furthermore, this will have implications for probabilistic impact risk assessment models.

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arXiv2023

Photometry of the Didymos system across the DART impact apparition

On 26 September 2022, the Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos. This demonstrated the efficacy of a kinetic impactor for planetary defense by changing the orbital period of Dimorphos by 33 minutes (Thomas et al. 2023). Measuring the period change relied heavily on a coordinated campaign of lightcurve photometry designed to detect mutual events (occultations and eclipses) as a direct probe of the satellite's orbital period. A total of 28 telescopes contributed 224 individual lightcurves during the impact apparition from July 2022 to February 2023. We focus here on decomposable lightcurves, i.e. those from which mutual events could be extracted. We describe our process of lightcurve decomposition and use that to release the full data set for future analysis. We leverage these data to place constraints on the post-impact evolution of ejecta. The measured depths of mutual events relative to models showed that the ejecta became optically thin within the first ~1 day after impact, and then faded with a decay time of about 25 days. The bulk magnitude of the system showed that ejecta no longer contributed measurable brightness enhancement after about 20 days post-impact. This bulk photometric behavior was not well represented by an HG photometric model. An HG1G2 model did fit the data well across a wide range of phase angles. Lastly, we note the presence of an ejecta tail through at least March 2023. Its persistence implied ongoing escape of ejecta from the system many months after DART impact.

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arXiv2023

Ejecta Evolution Following a Planned Impact into an Asteroid: The First Five Weeks

The impact of the DART spacecraft into Dimorphos, moon of the asteroid Didymos, changed Dimorphos' orbit substantially, largely from the ejection of material. We present results from twelve Earth-based facilities involved in a world-wide campaign to monitor the brightness and morphology of the ejecta in the first 35 days after impact. After an initial brightening of ~1.4 magnitudes, we find consistent dimming rates of 0.11-0.12 magnitudes/day in the first week, and 0.08-0.09 magnitudes/day over the entire study period. The system returned to its pre-impact brightness 24.3-25.3 days after impact through the primary ejecta tail remained. The dimming paused briefly eight days after impact, near in time to the appearance of the second tail. This was likely due to a secondary release of material after re-impact of a boulder released in the initial impact, through movement of the primary ejecta through the aperture likely played a role.

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arXiv2023

Orbital Period Change of Dimorphos Due to the DART Kinetic Impact

The Double Asteroid Redirection Test (DART) spacecraft successfully performed the first test of a kinetic impactor for asteroid deflection by impacting Dimorphos, the secondary of near-Earth binary asteroid (65803) Didymos, and changing the orbital period of Dimorphos. A change in orbital period of approximately 7 minutes was expected if the incident momentum from the DART spacecraft was directly transferred to the asteroid target in a perfectly inelastic collision, but studies of the probable impact conditions and asteroid properties indicated that a considerable momentum enhancement ($β$) was possible. In the years prior to impact, we used lightcurve observations to accurately determine the pre-impact orbit parameters of Dimorphos with respect to Didymos. Here we report the change in the orbital period of Dimorphos as a result of the DART kinetic impact to be -33.0 +/- 1.0 (3$σ$) minutes. Using new Earth-based lightcurve and radar observations, two independent approaches determined identical values for the change in the orbital period. This large orbit period change suggests that ejecta contributed a significant amount of momentum to the asteroid beyond what the DART spacecraft carried.

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arXiv2022

The Aligned Orbit of WASP-148b, the Only Known Hot Jupiter with a Nearby Warm Jupiter Companion, from NEID and HIRES

We present spectroscopic measurements of the Rossiter-McLaughlin effect for WASP-148b, the only known hot Jupiter with a nearby warm-Jupiter companion, from the WIYN/NEID and Keck/HIRES instruments. This is one of the first scientific results reported from the newly commissioned NEID spectrograph, as well as the second obliquity constraint for a hot Jupiter system with a close-in companion, after WASP-47. WASP-148b is consistent with being in alignment with the sky-projected spin axis of the host star, with $λ=-8^{\circ}.2^{{+8^{\circ}.7}}_{-9^{\circ}.7}$. The low obliquity observed in the WASP-148 system is consistent with the orderly-alignment configuration of most compact multi-planet systems around cool stars with obliquity constraints, including our solar system, and may point to an early history for these well-organized systems in which migration and accretion occurred in isolation, with relatively little disturbance. By contrast, previous results have indicated that high-mass and hot stars appear to more commonly host a wide range of misaligned planets: not only single hot Jupiters, but also compact systems with multiple super-Earths. We suggest that, to account for the high rate of spin-orbit misalignments in both compact multi-planet and isolated-hot-Jupiter systems orbiting high-mass and hot stars, spin-orbit misalignments may be caused by distant giant planet perturbers, which are most common around these stellar types.

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arXiv2022

Recent formation and likely cometary activity of near-Earth asteroid pair 2019 PR2 -- 2019 QR6

Asteroid pairs are genetically related asteroids that recently separated ($<$few million years), but still reside on similar heliocentric orbits. A few hundred of these systems have been identified, primarily in the asteroid main-belt. Here we studied a newly discovered pair of near-Earth objects (NEOs): 2019 PR2 and 2019 QR6. Based on broad-band photometry, we found these asteroids to be spectrally similar to D-types, a type rare amongst NEOs. We recovered astrometric observations for both asteroids from the Catalina Sky Survey from 2005, which significantly improved their fitted orbits. With these refinements we ran backwards orbital integrations to study formation and evolutionary history. We found that neither a pure gravitational model nor a model with the Yarkovsky effect could explain their current orbits. We thus implemented two models of comet-like non-gravitational forces based on water or CO sublimation. The first model assumed quasi-continuous, comet-like activity after separation, which suggested a formation time of the asteroid pair $300^{+120}_{-70}$ years ago. The second model assumed short-term activity for up to one heliocentric orbit ($\sim$13.9 years) after separation, which suggested that the pair formed 272$\pm$7 years ago. Image stacks showed no activity for 2019~PR2 during its last perihelion passage. These results strongly argue for a common origin that makes these objects the youngest asteroid pair known to date. Questions remain regarding whether these objects derived from a parent comet or asteroid, and how activity may have evolved since their separation.

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arXiv2021

Projected Rotational Velocities and Fundamental Properties of Low-Mass Pre-Main Sequence Stars in the Taurus-Auriga Star Forming Region

The projected stellar rotational velocity ($v \sin i$) is critical for our understanding of processes related to the evolution of angular momentum in pre-main sequence stars. We present $v \sin i$ measurements of high-resolution infrared and optical spectroscopy for 70 pre-main sequence stars in the Taurus-Auriga star-forming region, in addition to effective temperatures measured from line-depth ratios, and stellar rotation periods determined from optical photometry. From the literature, we identified the stars in our sample that show evidence of residing in circumstellar disks or multiple systems. The comparison of infrared $v \sin i$ measurements calculated using two techniques shows a residual scatter of $\sim$ 1.8 km s$^{-1}$, defining a typical error floor for the $v \sin i$ of pre-main sequence stars from infrared spectra. A comparison of the $v \sin i$ distributions of stars with and without companions shows that binaries/multiples typically have a higher measured $v \sin i$, which may be caused by contamination by companion lines, shorter disk lifetimes in binary systems, or tidal interactions in hierarchical triples. A comparison of optical and infrared $v \sin i$ values shows no significant difference regardless of whether the star has a disk or not, indicating that CO contamination from the disk does not impact $v \sin i$ measurements above the typical $\sim$ 1.8 km s$^{-1}$ error floor of our measurements. Finally, we observe a lack of a correlation between the $v \sin i$, presence of a disk, and H-R diagram position, which indicates a complex interplay between stellar rotation and evolution of pre-main sequence stars.

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arXiv2020

ACRONYM IV: Three New, Young, Low-mass Spectroscopic Binaries

As part of our search for new low-mass members of nearby young moving groups (YMG), we discovered three low-mass, spectroscopic binaries, two of which are not kinematically associated with any known YMG. Using high-resolution optical spectroscopy, we measure the component and systemic radial velocities of the systems, as well as their lithium absorption and H$α$ emission, both spectroscopic indicators of youth. One system (2MASS J02543316-5108313, M2.0+M3.0) we confirm as a member of the 40 Myr old Tuc-Hor moving group, but whose binarity was previously undetected. The second young binary (2MASS J08355977-3042306, K5.5+M1.5) is not a kinematic match to any known YMG, but each component exhibits lithium absorption and strong and wide H$α$ emission indicative of active accretion, setting an upper age limit of 15 Myr. The third system (2MASS J10260210-4105537, M1.0+M3.0) has been hypothesized in the literature to be a member of the 10 Myr old TW Hya Association (TWA), but with our measured systemic velocity, shows the binary is in fact not part of any known YMG. This last system also has lithium absorption in each component, and has strong and variable H$α$ emission, setting an upper age limit of 15 Myr based on the lithium detection.

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arXiv2019

Visible spectroscopy from the Mission Accessible Near-Earth Object Survey (MANOS): Taxonomic dependence on asteroid size

The Mission Accessible Near-Earth Object Survey (MANOS) aims to observe and characterize small (mean absolute magnitude H ~ 25 mag) Near-Earth Objects (NEOs) that are accessible by spacecraft (mean $Δv$ ~ 5.7 km/s) and that make close approaches with the Earth (mean Minimum Orbital Intersection Distance MOID ~ 0.03 AU). We present here the first results of the MANOS visible spectroscopic survey. The spectra were obtained from August 2013 to March 2018 at Lowell Observatory's Discovery Channel 4.3 meter telescope, and both Gemini North and South facilities. In total, 210 NEOs have been observed and taxonomically classified. Our taxonomic distribution shows significant variations with respect to surveys of larger objects. We suspect these to be due to a dependence of Main Belt source regions on object size. Compared to previous surveys of larger objects (Binzel et al. 2019, 2004; Perna et al. 2018), we report a lower fraction of S+Q-complex asteroids of 43.8 $\pm$ 4.6%. We associate this decrease with a lack of Phocaea family members at very small size. We also report higher fractions of X-complex and A-type asteroids of 23.8 $\pm$ 3.3% and 3.8 $\pm$ 1.3% respectively due to an increase of Hungaria family objects at small size. We find a strong correlation between the Q/S ratio and perihelion distance. We suggest this correlation is due to planetary close encounters with Venus playing a major role in turning asteroids from S to Q-type. This hypothesis is supported by a similar correlation between the Q/S ratio and Venus MOID.

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arXiv2019

Magnetic Inflation and Stellar Mass III: Revised Parameters for the Component Stars of NSVS 07394765

We perform a new analysis of the M dwarf-M dwarf eclipsing binary system NSVS 07394765 in order to investigate the reported hyper-inflated radius of one of the component stars. Our analysis is based on archival photometry from the Wide Angle Search for Planets (WASP), new photometry from the 32 cm {Command Module Observatory (CMO) telescope in Arizona and the 70 cm telescope at Thacher Observatory in California}, and new high-resolution infrared spectra obtained with the Immersion Grating Infrared Spectrograph (IGRINS) on the Discovery Channel Telescope. The masses and radii we measure for each component star disagree with previously reported measurements. We show that both stars are early M-type main-sequence stars without evidence for youth or hyper-inflation ($M_1= 0.661\ ^{+0.008}_{-0.036}\ \rm{M_{sun}}$, $M_2= 0.608\ ^{+0.003}_{-0.028}\ \rm{M_{sun}}$, $R_1= 0.599\ ^{+0.032}_{-0.019}\ \rm{R_{sun}}$, $R_2= 0.625\ ^{+0.012}_{-0.027}\ \rm{R_{sun}}$), and we update the orbital period and eclipse ephemerides for the system. We suggest that the likely cause of the initial hyper-inflated result is the use of moderate-resolution spectroscopy for precise radial velocity measurements.

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arXiv2019

A common origin for dynamically associated near-Earth asteroid pairs

Though pairs of dynamically associated asteroids in the Main Belt have been identified and studied for over a decade, very few pair systems have been identified in the near-Earth asteroid population. We present data and analysis that supports the existence of two genetically related pairs in near-Earth space. The members of the individual systems, 2015 EE7 -- 2015 FP124 and 2017 SN16 -- 2018 RY7, are found to be of the same spectral taxonomic class, and both pairs are interpreted to have volatile-poor compositions. In conjunction with dynamical arguments, this suggests that these two systems formed via YORP spin-up and/or dissociation of a binary precursor. Backwards orbital integrations suggest a separation age of <10 kyr for the pair 2017 SN16 -- 2018 RY7, making these objects amongst the youngest multiple asteroid systems known to date. A unique separation age was not realized for 2015 EE7 -- 2015 FP124 due to large uncertainties associated with these objects' orbits. Determining the ages of such young pairs is of great value for testing models of space weathering and asteroid spin-state evolution. As the NEO catalog continues to grow with current and future discovery surveys, it is expected that more NEO pairs will be found, thus providing an ideal laboratory for studying time dependent evolutionary processes that are relevant to asteroids throughout the Solar System.

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arXiv2018

A Runaway Giant in the Galactic Halo

New evidence provided by the Gaia satellite places the location of the runaway star J01020100-7122208 in the halo of the Milky Way (MW) rather than in the Small Magellanic Cloud as previously thought. We conduct a reanalysis of the star's physical and kinematic properties, which indicates that the star may be an even more extraordinary find than previously reported. The star is a 180 Myr old 3-4 Mo G5-8 bright giant, with an effective temperature of 4800+/-100 K, a metallicity of {Fe/H]=-0.5, and a luminosity of log L/Lo=2.70+/-0.20 dex. A comparison with evolutionary tracks identifies the star as being in a giant or early asymptotic giant branch stage. The proper motion, combined with the previously known radial velocity, yields a total Galactocentric space velocity of 296 km/s. The star is currently located 6.4 kpc below the plane of the Milky Way, but our analysis of its orbit shows it passed through the disk ~25 Myr ago. The star's metallicity and age argue against it being native to the halo, and we suggest that the star was likely ejected from the disk. We discuss several ejection mechanisms, and conclude that the most likely scenario is ejection by the Milky Way's central black hole based upon our analysis of the star's orbit. The identification of the large radial velocity of J01020100-7122208 came about as a happenstance of it being seen in projection with the SMC, and we suggest that many similar objects may be revealed in Gaia data.

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arXiv2018

A Runaway Yellow Supergiant Star in the Small Magellanic Cloud

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, consistent with it being a ~30Myr 9Mo star according to the Geneva evolution models. The star is currently located in the outer portion of the SMC's body, but if the star's transverse peculiar velocity is similar to its peculiar radial velocity, in 10Myr the star would have moved 1.6 degrees across the disk of the SMC, and could easily have been born in one of the SMC's star-forming regions. Based on its large radial velocity, we suggest it originated in a binary system where the primary exploded as a supernovae thus flinging the runaway star out into space. Such stars may provide an important mechanism for the dispersal of heavier elements in galaxies given the large percentage of massive stars that are runaways. In the future we hope to look into additional evolved runaway stars that were discovered as part of our other past surveys.

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arXiv2016

Results from the 2014 November 15th multi-chord stellar occultation by the TNO (229762) 2007 UK$_{126}$

We present results derived from the first multi-chord stellar occultation by the trans-Neptunian object (229762) 2007 UK$_{126}$, observed on 2014 November 15. The event was observed by the Research and Education Collaborative Occultation Network (RECON) project and International Occultation Timing Association (IOTA) collaborators throughout the United States. Use of two different data analysis methods obtain a satisfactory fit to seven chords, yelding an elliptical fit to the chords with an equatorial radius of $R=338_{-10} ^{+15}$ km and equivalent radius of $R_{eq}=319_{-7} ^{+14}$ km. A circular fit also gives a radius of $R=324_{-23} ^{+30}$ km. Assuming that the object is a Maclaurin spheroid with indeterminate aspect angle, and using two published absolute magnitudes for the body, we derive possible ranges for geometric albedo between $p_{V}=0.159_{-0.013} ^{+0.007}$ and $p_{R}=0.189_{-0.015}^{+0.009}$, and for the body oblateness between $ε=0.105_{-0.040} ^{+0.050}$ and $ε=0.118_{-0.048} ^{+0.055}$. For a nominal rotational period of 11.05 h, an upper limit for density of $ρ=1740$ kg~m$^{-3}$ is estimated for the body.

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arXiv2015

Link between the Potentially Hazardous Asteroid (86039) 1999 NC43 and the Chelyabinsk meteoroid tenuous

We explored the statistical and compositional link between Chelyabinsk meteoroid and potentially hazardous asteroid (86039) 1999 NC43 to investigate their proposed relation proposed by Borovička et al. (2013). Using detailed computation we confirm that the orbit of the Chelyabinsk impactor is anomalously close to 1999 NC43. We find about (1-3) x 10-4 likelihood of that to happen by chance. Taking the standpoint that the Chelyabinsk impactor indeed separated from 1999 NC43 by a cratering or rotational fission event, we run a forward probability calculation, which is an independent statistical test. However, we find this scenario is unlikely at the about (10-3 -10-2) level. We also verified compositional link between Chelyabinska and 1999NC43. Mineralogical analysis of Chelyabinsk (LL chondrite) and (8) Flora (the largest member of the presumed LL chondrite parent family) shows that their olivine and pyroxene chemistries are similar to LL chondrites. Similar analysis of 1999 NC43 shows that its olivine and pyroxene chemistries are more similar to L chondrites than LL chondrites (like Chelyabinsk). We also took photometric observations of 1999 NC43 over 54 nights during two apparitions (2000, 2014). The lightcurve of 1999 NC43 resembles simulated lightcurves of tumblers in Short-Axis Mode with the mean wobbling angle 20-30 deg. While, a mechanism of the non-principal axis rotation excitation is unclear, we can rule out the formation of asteroid in disruption of its parent body as a plausible cause, as it is unlikely that the rotation of an asteroid fragment from catastrophic disruption would be nearly completely halted. Considering all these facts, we find the proposed link between the Chelyabinsk meteoroid and the asteroid 1999 NC43 to be unlikely.

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arXiv2013

Orbital Parameters for the Two Young Binaries VSB 111 and VSB 126

We report orbital parameters for two low-mass, pre-main sequence, double-lined spectroscopic binaries VSB 111 and VSB 126. These systems were originally identified as single-lined on the basis of visible-light observations. We obtained high-resolution, infrared spectra with the 10-m Keck II telescope, detected absorption lines of the secondary stars, and measured radial velocities of both components in the systems. The visible light spectra were obtained on the 1.5-m Wyeth reflector at the Oak Ridge Observatory, the 1.5-m Tillinghast reflector at the F. L. Whipple Observatory, and the 4.5-m equivalent Multiple Mirror Telescope. The combination of our visible and infrared observations of VSB 111 leads to a period of 902.1+/-0.9 days, an eccentricity of 0.788+/-0.008, and a mass ratio of 0.52+/-0.05. VSB 126 has a period of 12.9244+/-0.0002 days, an eccentricity of 0.18+/-0.02, and a mass ratio of 0.29+/-0.02. Visible-light photometry, using the 0.8-m telescope at Lowell Observatory, provided rotation periods for the primary stars in both systems, 3.74+/-0.02 days for VSB 111 and 5.71+/-0.07 days for VSB 126. Both binaries are located in the young, active star-forming cluster NGC 2264 at a distance of ~800 pc. The difference in the center-of-mass velocities of the two systems is consistent with the radial velocity gradient seen across NGC 2264. To test the evolutionary models for accuracy and consistency, we compare the stellar properties derived from several sets of theoretical calculations for pre-main sequence evolution with our dynamical results.

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arXiv2012

Yellow and Red Supergiants in the Large Magellanic Cloud

Due to their transitionary nature, yellow supergiants provide a critical challenge for evolutionary modeling. Previous studies within M31 and the SMC show that the Geneva evolutionary models do a poor job at predicting the lifetimes of these short-lived stars. Here we extend this study to the LMC while also investigating the galaxy's red supergiant content. This task is complicated by contamination by Galactic foreground stars that color and magnitude criteria alone cannot weed out. Therefore, we use proper motions and the LMC's large systemic radial velocity (\sim278 km/s) to separate out these foreground dwarfs. After observing nearly 2,000 stars, we identified 317 probable yellow supergiants, 6 possible yellow supergiants and 505 probable red supergiants. Foreground contamination of our yellow supergiant sample was \sim80%, while that of the the red supergiant sample was only 3%. By placing the yellow supergiants on the H-R diagram and comparing them against the evolutionary tracks, we find that new Geneva evolutionary models do an exemplary job at predicting both the locations and the lifetimes of these transitory objects.

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arXiv2010

Yellow Supergiants in the Small Magellanic Cloud (SMC): Putting Current Evolutionary Theory to the Test

The yellow supergiant content of nearby galaxies provides a critical test of massive star evolutionary theory. While these stars are the brightest in a galaxy, they are difficult to identify because a large number of foreground Milky Way stars have similar colors and magnitudes. We previously conducted a census of yellow supergiants within M31 and found that the evolutionary tracks predict a yellow supergiant duration an order of magnitude longer than we observed. Here we turn our attention to the SMC, where the metallicity is 10x lower than that of M31, which is important as metallicity strongly affects massive star evolution. The SMC's large radial velocity (~160 km/s) allows us to separate members from foreground stars. Observations of ~500 candidates yielded 176 near-certain SMC supergiants, 16 possible SMC supergiants, along with 306 foreground stars and provide good relative numbers of yellow supergiants down to 12Mo. Of the 176 near-certain SMC supergiants, the kinematics predicted by the Besancon model of the Milky Way suggest a foreground contamination of >4%. After placing the SMC supergiants on the H-R diagram and comparing our results to the Geneva evolutionary tracks, we find results similar to those of the M31 study: while the locations of the stars on the H-R diagram match the locations of evolutionary tracks well, the models over-predict the yellow supergiant lifetime by a factor of ten. Uncertainties about the mass-loss rates on the main-sequence thus cannot be the primary problem with the models.

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