arXiv 1808.02618: Earth and Planetary Astrophysics OSSOS: XIII. Fossilized Resonant Dropouts Imply Neptune's Migration was Grainy and Slow

Paper: OSSOS: XIII. Fossilized Resonant Dropouts Imply Neptune's Migration was Grainy and Slow
Authors: S. M. Lawler, R. E. Pike, N. Kaib, M. Alexandersen, M. T. Bannister, Y.-T. Chen, B. Gladman, S. Gwyn, J. J. Kavelaars, J.-M. Petit, K. Volk

Abstract: The migration of Neptune's resonances through the early Kuiper belt has left signatures of the migration timescale and mode in the distribution of small bodies in the outer Solar System. Here we analyze five published Neptune migration models in detail, focusing on the high pericenter distance (q) trans-Neptunian Objects (TNOs) near Neptune's mean-motion resonances. We focus on the TNOs near the 5:2 and 3:1 resonances, because they have large detected populations, are outside the main classical belt, and are relatively isolated from other strong resonances. We compare the observationally biased output from these dynamical models with the detected TNOs from the Outer Solar System Origins Survey, via its Survey Simulator. All of the four new OSSOS detections of high-q non-resonant TNOs are on the Sunward side of the 5:2 and 3:1 resonances. We show that even after accounting for observation biases, this asymmetric distribution cannot be drawn from a uniform distribution of TNOs at 2-sigma confidence. We find that the dynamical model that uses grainy slow Neptune migration provides the best match to the real TNO orbital data. However, due to extreme observational biases, we have very few high pericenter distance TNO discoveries with which to statistically constrain the models. We show that a deeper survey (to a limiting r-magnitude of 26.0) with a similar survey area to OSSOS could statistically distinguish between these five Neptune migration models. We speculate that the cycle of resonance sticking and Kozai oscillation within a resonance, followed by resonant dropout into this fossilized high-q population, could potentially explain all but the two very highest-q TNOs discovered to date.

My Comment: To me this is so very much the heart of astronomy science. We very rarely can do an experiment in the lab, so we have to do as much as possible with what we are able to observe. Our theories must be realized by careful simulation of what the physics say they do, and then must be carefull compared to well-characterized observations.

My Scrawling Notes:

arXiv:1808.01862: Yes, Aboriginal Australians Can and Did Discover the Variability of Betelgeuse

Paper: Yes, Aboriginal Australians Can and Did Discover the Variability of Betelgeuse
Authors: Bradley E. Schaefer

Abstract: Recently, a widely publicized claim has been made that the Aboriginal Australians discovered the variability of the red star Betelgeuse in the modern Orion, plus the variability of two other prominent red stars: Aldebaran and Antares. This result has excited the usual healthy skepticism, with questions about whether any untrained peoples can discover the variability and whether such a discovery is likely to be placed into lore and transmitted for long periods of time. Here, I am offering an independent evaluation, based on broad experience with naked-eye sky viewing and astro-history. I find that it is easy for inexperienced observers to detect the variability of Betelgeuse over its range in brightness from V = 0.0 to V = 1.3, for example in noticing from season-to-season that the star varies from significantly brighter than Procyon to being greatly fainter than Procyon. Further, indigenous peoples in the Southern Hemisphere inevitably kept watch on the prominent red star, so it is inevitable that the variability of Betelgeuse was discovered many times over during the last 65 millennia. The processes of placing this discovery into a cultural context (in this case, put into morality stories) and the faithful transmission for many millennia is confidently known for the Aboriginal Australians in particular. So this shows that the whole claim for a changing Betelgeuse in the Aboriginal Australian lore is both plausible and likely. Given that the discovery and transmission is easily possible, the real proof is that the Aboriginal lore gives an unambiguous statement that these stars do indeed vary in brightness, as collected by many ethnographers over a century ago from many Aboriginal groups. So I strongly conclude that the Aboriginal Australians could and did discover the variability of Betelgeuse, Aldebaran, and Antares.

My Comment: The title of this paper caught my eye, as a student was doing an astro-education project on the variability of Betelgeuse. She had various peoples, typically untrained observers, and children, observe Betelgeuse for variability, and the early results indicated that it was easily accomplished. This fact of it being an easily observable thing to "discover" was a central point in the paper. In no way is the claim of Aboriginal Australians discovering the variability of Betelgeuse "fantastic." This article tells a clear and direct narrative that lays out the evidence, analysis, and methodology involved, and show how to investigate claims of real cultural knowledge in the era of fantastical claims. 

My Scrawling Notes:

arXiv:1808.00609 - The excitation of a primordial cold asteroid belt as an outcome of the planetary instability

Paper: The excitation of a primordial cold asteroid belt as an outcome of the planetary instability
Authors: Rogerio Deienno, Andre Izidoro, Alessandro Morbidelli, Rodney S. Gomes, David Nesvorny, Sean N. Raymond

Abstract: The main asteroid belt (MB) is low in mass but dynamically excited. Here we propose a new mechanism to excite the MB during the giant planet ('Nice model') instability, which is expected to have featured repeated close encounters between Jupiter and one or more ice giants ('Jumping Jupiter' -- JJ). We show that, when Jupiter temporarily reaches a high enough level of excitation, both in eccentricity and inclination it induces strong forced vectors of eccentricity and inclination across the MB region. Because during the JJ instability Jupiter's orbit `jumps' around, the forced vectors keep changing both in magnitude and phase throughout the whole MB region. The entire cold primordial MB is thus excited as a natural outcome of the JJ instability. The level of such an excitation, however, is typically larger than the current orbital excitation observed in the MB. We show that the subsequent evolution of the Solar System is capable of reshaping the resultant over-excited MB to its present day orbital state, and that a strong mass depletion (∼90%) is associated to the JJ instability phase and its subsequent evolution throughout the age of the Solar System

My Comment: Solar System dynamics are what drew me into astronomy in the first place. More than any results of this paper, I find it absolutely stellar as it clearly explains what is being simulated, and why, and points the reader at additional sources of information on the particulars. In sense it manages to not only present the science that was done, but also how that science was accomplished.

My Scrawling Notes:

arXiv:1807.11496 - Gaia: Orion's Integral Shaped Filament is a Standing Wave

Paper: Gaia: Orion's Integral Shaped Filament is a Standing Wave
Authors: Amelia M. Stutz, Valentina I. Gonzalez-Lobos, Andrew Gould

Abstract: The Integral Shaped Filament (ISF) is the nearest molecular cloud with rapid star formation, including massive stars, and it is therefore a star-formation laboratory. We use Gaia parallaxes, to show that the distances to young Class II stars ('disks') projected along the spine of this filament are related to the gas radial velocity by

v=−Dτ+K;τ=4Myr,

where K is a constant. This implies that the ISF is a standing wave, which is consistent with the Stutz & Gould (2016) 'Slingshot' prediction. The τ=4Myr timescale is consistent with the 'Slingshot' picture that the Orion Nebula Cluster (ONC) is the third cluster to be violently split off from the Orion A cloud (following NGC 1981 and NGC 1987) at few-Myr intervals due to gravito-magnetic oscillations. We also present preliminary evidence that the truncation of the ISF is now taking place 16′ south of the ONC and is mediated by a torsional wave that is propagating south with a characteristic timescale τtorsion=0.5Myr, i.e. eight times shorter. The relation between these two wave phenomena is not presently understood.

My Comment: Dear students: this (one reason) why it is important to understand simple waves. 

My Scrawling Notes:

arXiv:1807.11442 - A Catalog of Spectra, Albedos, and Colors of Solar System Bodies for Exoplanet Comparison

Paper: A Catalog of Spectra, Albedos, and Colors of Solar System Bodies for Exoplanet Comparison
Authors: J. H. Madden, Lisa Kaltenegger

Abstract: We present a catalog of spectra and geometric albedos, representative of the different types of Solar System bodies, from 0.45 to 2.5 microns. We analyzed published calibrated, un-calibrated spectra, and albedos for Solar System objects and derived a set of reference spectra and reference albedo for 19 objects that are representative of the diversity of bodies in our Solar System. We also identified previously published data that appears contaminated. Our catalog provides a baseline for comparison of exoplanet observations to 19 bodies in our own Solar System, which can assist in the prioritization of exoplanets for time-intensive follow-up with next-generation Extremely Large Telescopes (ELTs) and space-based direct observation missions. Using high and low-resolution spectra of these Solar System objects, we also derive colors for these bodies and explore how a color-color diagram could be used to initially distinguish between rocky, icy, and gaseous exoplanets. We explore how the colors of Solar System analog bodies would change when orbiting different host stars. This catalog of Solar System reference spectra and albedos is available for download through the Carl Sagan Institute.

My Comment: This is cool stuff. In order to have a clue as to what we will (soon) be looking at in terms of exoplanets we need to know what the worlds that we have access to would look like as exoworlds. This (public) catalog is a nice first step. Clearly acknowledging several issues that arose in making it, it lays out a nice guideline as to how to make a first-pass at guessing if you are looking at a rocky or icy surface, or at a whole bunch of gas.  Also: Venus is hard.

My Scrawling Notes:

arXiv:1807.10612 - Cluster kinematics and stellar rotation in NGC 419 with MUSE and adaptive optics

Paper: Cluster kinematics and stellar rotation in NGC 419 with MUSE and adaptive optics
Authors: Sebastian Kamann, Nathan J. Bastian, Tim-Oliver Husser, Silvia Martocchia, Christopher Usher, Mark den Brok, Stefan Dreizler, Andreas Kelz, Davor Krajnović, Johan Richard, Matthias Steinmetz, Peter M. Weilbacher

Abstract: We present adaptive optics (AO) assisted integral-field spectroscopy of the intermediate-age star cluster NGC 419 in the Small Magellanic Cloud. By investigating the cluster dynamics and the rotation properties of main sequence turn-off stars (MSTO), we demonstrate the power of AO-fed MUSE observations for this class of objects. Based on 1 049 radial velocity measurements, we determine a dynamical cluster mass of 1.4+/-0.2x10^5 M_sun and a dynamical mass-to-light ratio of 0.67+/-0.08, marginally higher than simple stellar population predictions for a Kroupa initial mass function. A stacking analysis of spectra at both sides of the extended MSTO reveals significant rotational broadening. Our analysis further provides tentative evidence that red MSTO stars rotate faster than their blue counterparts. We find average V sin i values of 87+/-16 km/s and 130+/-22 km/s for blue and red MSTO stars, respectively. Potential systematic effects due to the low spectral resolution of MUSE can reach 30 km/s but the difference in V sin i between the populations is unlikely to be affected.

My Comment: The first two "research" assignments I ever had in graduate school involved star clusters and cluster dynamics. This was a bit perplexing as I was looking to work on solar system dynamics, and only knew that a "cluster" was a group of gravitationally bound stars from reading through an introductory astronomy text prior to being a TA; the only serious astronomy I had done as an undergrad was to work out the transformations of taking earth-based observations into orbits. 

My Scrawling Notes:

arXiv:1807.09806 -- Young and eccentric: the quadruple system HD 86588

Paper: Young and eccentric: the quadruple system HD 86588
Authors: Andrei Tokovinin, Hank Corbett, Octavi Fors, Ward Howard, Nicholas M. Law, Maxwell Moe, Frederick M. Walter

Abstract: High-resolution spectroscopy and speckle interferometry reveal the young star HD 86588 as a quadruple system with a 3-tier hierarchy. The 0.3" resolved binary A,B with an estimated period around 300 years contains the 8-year pair Aa,Abc (also potentially resolvable), where Ab,Ac is a double-lined binary with equal components, for which we compute the spectroscopic orbit. Despite the short period of 2.4058 day, the orbit of Ab,Ac is eccentric (e=0.086+-0.003). It has a large inclination, but there are no eclipses; only a 4.4 mmag light modulation apparently caused by star spots on the components of this binary is detected with Evryscope. Assuming a moderate extinction of A_V = 0.5 mag and a parallax of 5.2 mas, we find that the stars are on or close to the main sequence (age >10 Myr) and their masses are from 1 to 1.3 solar. We measure the strength of the Lithium line in the visual secondary B which, together with rotation, suggests that the system is younger than 150 Myr. This object is located behind the extension of the Chamaeleon I dark cloud (which explains extinction and interstellar Sodium absorption), but apparently does not belong to it. We propose a scenario where the inner orbit has recently acquired its high eccentricity through dynamical interaction with the outer two components; it is now undergoing rapid tidal circularization on a time scale of ~1 Myr. Alternatively, the eccentricity could be excited quasi-stationary by the outer component Aa.

My Comment: I love crazy dynamical systems. Two stars orbit each other as a binary. That binary orbits with another star as a compound binary. That compound (3-star) binary orbits with yet another star, making the whole system a three-level binary set of four stars. Really neat stuff.

My Scrawling Notes:

arXiv:1807.08322 -- Pre-airburst Orbital Evolution of Earth's Impactor 2018 LA: An Update

Paper: Pre-airburst Orbital Evolution of Earth's Impactor 2018 LA: An Update
Authors:C. de la Fuente Marcos, R. de la Fuente Marcos 

Abstract: Apollo meteoroid 2018 LA has become only the third natural object ever to be discovered prior to causing a meteor airburst and just the second one to have its meteorites recovered (at Botswana's Central Kalahari Game Reserve). Here, we use the latest orbit determination of 2018 LA (solution date 18-July-2018) to search for minor bodies moving in paths comparable to that of 2018 LA using the D-criteria, which are metrics to study orbit similarity, and N-body simulations. Our results further confirm the existence of a dynamical grouping of asteroids that might be related to 2018 LA and show that the impactor could be a recent fragment spawned by a larger object, the 550-m wide, potentially hazardous asteroid (454100) 2013 BO73. Spectroscopic observations of 454100 during its next flyby with our planet (brightest at an apparent visual magnitude of 18.4 on 2018 mid-November) may confirm or deny a putative similar chemical composition to that of the recovered meteorites of 2018 LA.

My Comment: A second very short letter (busy week this), but it does something very remarkable, very hard, and very needed -- attempting to link the space rocks on the ground to the rocks in space. For the most part all we can do is try to match spectra of meteorite samples in the lab to the reflectance spectra of asteroids in space. It is filled with many pitfalls. This is really neat as it gives a second diagnostic tool to work with - the dynamics of the impactor's orbit.

My Scrawling Notes:

arXiv:1807.08728 -- P/2017 S5: Another Active Asteroid Associated with the Theobalda Family

Paper: P/2017 S5: Another Active Asteroid Associated with the Theobalda Family
Authors: Bojan Novakovic

Abstract: In this note we have shown that a newly discovered comet P/2017 S5 (ATLAS), that moves around the Sun in an asteroid-like orbit, is a member of the Theobalda asteroid family.

My Comment: Super short letter, but packed full of references giving a clear "how you do this science" outline. Love it. One of my favorite experiences with an undergrad research student was when she serendipitously found a candidate active asteroid while working with me on a comet project. Turns out it (most likely) wasn't but working out that puzzle involved her getting time on a 3.5m telescope(!), and having her work praised by Jocelyn Bell Burnell(!!).

My Scrawling Notes:

arXiv:1807.07557 -- WASP-128b: a transiting brown dwarf in the dynamical-tide regime

Paper: WASP-128b: a transiting brown dwarf in the dynamical-tide regime
Authors: V. Hodžić, et al.

Abstract: Massive companions in close orbits around G dwarfs are thought to undergo rapid orbital decay due to runaway tidal dissipation. We report here the discovery of WASP-128b, a brown dwarf discovered by the WASP survey transiting a G0V host on a 2.2d orbit, where the measured stellar rotation rate places the companion in a regime where tidal interaction is dominated by dynamical tides. Under the assumption of dynamical equilibrium, we derive a value of the stellar tidal quality factor logQ′⋆=6.96±0.19. A combined analysis of ground-based photometry and high-resolution spectroscopy reveals a mass and radius of the host, M⋆=1.16±0.04M⊙, R⋆=1.16±0.02R⊙, and for the companion, Mb=37.5±0.8MJup, Rb=0.94±0.02RJup, placing WASP-128b in the driest parts of the brown dwarf desert, and suggesting a mild inflation for its age. We estimate a remaining lifetime for WASP-128b similar to that of some ultra-short period massive hot Jupiters.

My Comment: I honestly didn't know (or had forgotten) that brown dwarf companions were very rare around solarish stars. I enjoyed the mix of observations, dynamic theory, and computational modelling all nicely fit together.

My Scrawling Notes:

arXiv:1807.06368 -- Planetary Nebulae distances in GAIA DR2

Paper: Planetary Nebulae distances in GAIA DR2
Authors: Stefan Kimeswenger, Daniela Barría

Abstract: Context: Planetary Nebula distance scales often suffer for model dependent solutions. Model independent trigonometric parallaxes have been rare. Space based trigonometric parallaxes are now available for a larger sample using the second data release of GAIA. 

Aims: We aim to derive a high quality approach for selection criteria of trigonometric parallaxes for planetary nebulae and discuss possible caveats and restrictions in the use of this data release. 

Methods: A few hundred sources from previous distance scale surveys were manually cross identified with data from the second GAIA data release (DR2) as coordinate based matching does not work reliable. The data are compared with the results of previous distance scales and to the results of a recent similar study, which was using the first data release GAIA DR1. 

Results: While the few available previous ground based and HST trigonometric parallaxes match perfectly to the new data sets, older statistical distance scales, reaching larger distances, do show small systematic differences. Restricting to those central stars, were photometric colors of GAIA show a negligible contamination by the surrounding nebula, the difference is negligible for radio flux based statistical distances, while those derived from H-alpha surface brightness still show minor differences. The DR2 study significantly improves the previous recalibration of the statistical distance scales using DR1/TGAS.

My Comment: Had not really though about it much before, but planetary nebula being big ol' clouds of gas are really tricky to measure distances to, if one is lucky you can find an embedded point-source that isn't suffering observationally from the surrounding gas. GAIA DR2, which is redefining our knowledge of our galaxy right now actually gives negative(!) parallaxes for many of these objects because space is hard.

My Scrawling Notes: (color and thumb avoidance fail today!)

arXiv:1807.05965 -- The Cow: discovery of a luminous, hot and rapidly evolving transient

Paper: The Cow: discovery of a luminous, hot and rapidly evolving transient
Authors: S. J. Prentice, et al.

Abstract: We present the ATLAS discovery and initial analysis of the first 18 days of the unusual transient event, ATLAS18qqn/AT2018cow. It is characeterized by a high peak luminosity (∼1.7×1044 erg s−1), rapidly evolving light curves (>5 mag rise in ∼3 days), hot blackbody spectra, peaking at ∼27000 K that are relatively featureless and unchanging over the first two weeks. The bolometric light curve cannot be powered by radioactive decay under realistic assumptions. The detection of high-energy emission may suggest a central engine as the powering source. Using a magnetar model, we estimated an ejected mass of 0.1−0.4 M⊙, which lies between that of low-energy core-collapse events and the kilonova, AT2017gfo. The spectra of AT2018cow showed a number of shallow features overlying a blackbody continuum. The spectra cooled rapidly from 27000 to 15000 K in just over 2 weeks but the positions of shallow bumps in the spectra did not evolve, suggesting that they are produced in a shell or are potentially emission features. Using spectral modelling, we tentatively identify some features as being due to He I and He II and rule out that the features in the spectra are due to most elements up to and including the Fe-group. The presence of r-process elements cannot be ruled out. If these lines are due to He, then we suggest a low-mass star with residual He as a potential progenitor. Alternatively, models of magnetars formed in neutron-star mergers give plausible matches to the data. 

My Comment: Weird things that go bump in the night are always neat. This object seems to offer some unique challenges (spectra) in terms of matching what it is. Best guess being a magnetar-like object. The combination of Cow and magnetar is honestly why this paper was chosen. Moooooo.

My Scrawling Notes:

arXiv:1807.02960 -- Outer solar system possibly shaped by a stellar fly-by

Paper: Outer solar system possibly shaped by a stellar fly-by
Authors: Susanne Pfalzner, Asmita Bhandare, Kirsten Vincke, Pedro Lacerda

Abstract: The planets of our solar system formed from a gas-dust disk. However, there are some properties of the solar system that are peculiar in this context. First, the cumulative mass of all objects beyond Neptune (TNOs) is only a fraction of what one would expect. Second, unlike the planets themselves, the TNOs do not orbit on coplanar, circular orbits around the Sun, but move mostly on inclined, eccentric orbits and are distributed in a complex way. This implies that some process restructured the outer solar system after its formation. However, some of TNOs, referred to as Sednoids, move outside the zone of influence of the planets. Thus external forces must have played an important part in the restructuring of the outer solar system. The study presented here shows that a close fly-by of a neighbouring star can simultaneously lead to the observed lower mass density outside 30 AU and excite the TNOs onto eccentric, inclined orbits, including the family of Sednoids. In the past it was estimated that such close fly-bys are rare during the relevant development stage. However, our numerical simulations show that such a scenario is much more likely than previously anticipated. A fly-by also naturally explains the puzzling fact that Neptune has a higher mass than Uranus. Our simulations suggest that many additional Sednoids at high inclinations still await discovery, perhaps including bodies like the postulated planet X.

My Comment: Fun discussion of solar system shaping mechanism and conducted further work to show plausibility of a fly-by during very early (10Myr) Solar System. Got me thinking about the Tisserand parameter with respect to Neptune, and once again am very happy to have astro-twitter folks willing to point papers and ideas out to me!

My Scrawling Notes:

Further investigation of changes in cometary rotation: arXiv:1806.11158

Paper: Further investigation of changes in cometary rotation
Authors: Beatrice E. A. Mueller, Nalin H. Samarasinha

Abstract: Samarasinha & Mueller (2013) related changes of cometary rotation to other physical parameters for four Jupiter family comets defining a parameter X  , which is approximately constant within a factor of two irrespective of the active fraction of a comet. Two additional comets are added to this sample in this paper and the claim of a nearly constant parameter X  for these six comets is confirmed, albeit with a larger scatter. Taking the geometric mean of X  for all the comets above excluding 2P/Encke (as X  for each comet was determined with respect to that of 2P/Encke), the expected changes in the rotation periods for a sample of 24 periodic comets are derived. We identify comets from this sample that are most likely to show observationally detectable changes in their rotation periods. Using this sample and including the six comets used to determine X  , we find a correlation between the parameter ζ  (i.e. the total water production per unit surface area per orbit approximated by that inside of 4 au) and the perihelion distance q  ; specifically we derive ζ  ∝  q −0.8   and provide a theoretical basis for this in Appendix A. This relationship between ζ  and q  enables ready comparisons of activity due to insolation between comets. Additionally, a relationship between the nuclear radius R  and the rotation period P  is found. Specifically, we find that on average smaller nuclei have smaller rotation periods compared to the rotation periods of larger nuclei. This is consistent with expectations for rotational evolution and spin-up of comet nuclei, providing strong observational evidence for sublimation-driven rotational changes in comets.

My Comment: The empirical law given seems to work on a factor of a few, which is better than the order of magnitude spanning effects being modeled. This paper does not justify its creation, with the details being presented in an earlier work from the authors in 2013.

My Scrawling Notes: