67 research outputs found
TRIPPy: Trailed Image Photometry in Python
Photometry of moving sources typically suffers from reduced signal-to-noise
(SNR) or flux measurements biased to incorrect low values through the use of
circular apertures. To address this issue we present the software package,
TRIPPy: TRailed Image Photometry in Python. TRIPPy introduces the pill
aperture, which is the natural extension of the circular aperture appropriate
for linearly trailed sources. The pill shape is a rectangle with two
semicircular end-caps, and is described by three parameters, the trail length
and angle, and the radius. The TRIPPy software package also includes a new
technique to generate accurate model point-spread functions (PSF) and trailed
point-spread functions (TSF) from stationary background sources in sidereally
tracked images. The TSF is merely the convolution of the model PSF, which
consists of a moffat profile, and super sampled lookup table. From the TSF,
accurate pill aperture corrections can be estimated as a function of pill
radius with a accuracy of 10 millimags for highly trailed sources. Analogous to
the use of small circular apertures and associated aperture corrections, small
radius pill apertures can be used to preserve signal-to-noise of low flux
sources, with appropriate aperture correction applied to provide an accurate,
unbiased flux measurement at all SNR.Comment: 8 Figures, 11 Pages, Accepted to the Astronomical Journa
Col-OSSOS: Colors of the Interstellar Planetesimal 1I/`Oumuamua
The recent discovery by Pan-STARRS1 of 1I/2017 U1 (`Oumuamua), on an unbound
and hyperbolic orbit, offers a rare opportunity to explore the planetary
formation processes of other stars, and the effect of the interstellar
environment on a planetesimal surface. 1I/`Oumuamua's close encounter with the
inner Solar System in 2017 October was a unique chance to make observations
matching those used to characterize the small-body populations of our own Solar
System. We present near-simultaneous g, r, and J photometry
and colors of 1I/`Oumuamua from the 8.1-m Frederick C. Gillett Gemini North
Telescope, and photometry from the 4.2 m William Herschel Telescope. Our
grJ observations are directly comparable to those from the
high-precision Colours of the Outer Solar System Origins Survey (Col-OSSOS),
which offer unique diagnostic information for distinguishing between outer
Solar System surfaces. The J-band data also provide the highest signal-to-noise
measurements made of 1I/`Oumuamua in the near-infrared. Substantial, correlated
near-infrared and optical variability is present, with the same trend in both
near-infrared and optical. Our observations are consistent with 1I/`Oumuamua
rotating with a double-peaked period of hours and being a
highly elongated body with an axial ratio of at least 5.3:1, implying that it
has significant internal cohesion. The color of the first interstellar
planetesimal is at the neutral end of the range of Solar System and
solar-reflectance colors: it is like that of some dynamically excited objects
in the Kuiper belt and the less-red Jupiter Trojans.Comment: Accepted to ApJ
Col-OSSOS: The Colours of the Outer Solar System Origins Survey
The Colours of the Outer Solar System Origins Survey (Col-OSSOS) is acquiring
near-simultaneous , , and photometry of unprecedented precision with
the Gemini North Telescope, targeting nearly a hundred trans-Neptunian objects
(TNOs) brighter than mag discovered in the Outer Solar System
Origins Survey. Combining the optical and near-infrared photometry with the
well-characterized detection efficiency of the Col-OSSOS target sample will
provide the first flux-limited compositional dynamical map of the outer Solar
System. In this paper, we describe our observing strategy and detail the data
reduction processes we employ, including techniques to mitigate the impact of
rotational variability. We present optical and near-infrared colors for 35
TNOs. We find two taxonomic groups for the dynamically excited TNOs, the
neutral and red classes, which divide at . Based on simple
albedo and orbital distribution assumptions, we find that the neutral class
outnumbers the red class, with a ratio of 4:1 and potentially as high as 11:1.
Including in our analysis constraints from the cold classical objects, which
are known to exhibit unique albedos and colors, we find that within our
measurement uncertainty, our observations are consistent with the primordial
Solar System protoplanetesimal disk being neutral-class-dominated, with two
major compositional divisions in color space.Comment: Accepted to ApJS; on-line supplemental files will be available with
the AJS published version of the pape
VLT/SPHERE observations and shape reconstruction of asteroid (6) Hebe
(6) Hebe is a large main-belt asteroid, accounting for about half a percent of the mass of the asteroid belt. Its spectral characteristics and close proximity to dynamical resonances within the main-belt (the 3:1 Kirkwood gap and the nu6 resonance) make it a probable parent body of the H-chondrites and IIE iron meteorites found on Earth.We present new AO images of Hebe obtained with the high-contrast imager SPHERE (Beuzit et al. 2008) as part of the science verification of the instrument. Hebe was observed close to its opposition date and throughout its rotation in order to derive its 3-D shape, and to allow a study of its surface craters. Our observations reveal impact zones that witness a severe collisional disruption for this asteroid. When combined to previous AO images and available lightcurves (both from the literature and from recent optical observations by our team), these new observations allow us to derive a reliable shape model using our KOALA algorithm (Carry et al. 2010). We further derive an estimate of Hebe's density based on its known astrometric mass
Twenty years of SpeX: Accuracy limits of spectral slope measurements in asteroid spectroscopy
We examined two decades of SpeX/NASA Infrared Telescope Facility observations
from the Small Main-Belt Asteroid Spectroscopic Survey (SMASS) and the
MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS) to investigate
uncertainties and systematic errors in reflectance spectral slope measurements
of asteroids. From 628 spectra of 11 solar analogs used for calibration of the
asteroid spectra, we derived an uncertainty of 4.2%/micron on slope
measurements over 0.8 to 2.4 micron. Air mass contributes to -0.92%/micron per
0.1 unit air mass difference between the asteroid and the solar analog, and
therefore for an overall 2.8%/micron slope variability in SMASS and MITHNEOS
designed to operate within 1.0 to 1.3 air mass. No additional observing
conditions (including parallactic angle, seeing and humidity) were found to
contribute systematically to slope change. We discuss implications for asteroid
taxonomic classification works. Uncertainties provided in this study should be
accounted for in future compositional investigation of small bodies to
distinguish intrinsic heterogeneities from possible instrumental effects.Comment: 15 pages, 11 figures, accepted for publication in ApJ
Col-OSSOS: The Distribution of Surface Classes in Neptune's Resonances
The distribution of surface classes of resonant trans-Neptunian objects
(TNOs) provides constraints on the protoplanetesimal disk and giant planet
migration. To better understand the surfaces of TNOs, the Colours of the Outer
Solar System Origins Survey (Col-OSSOS) acquired multi-band photometry of 102
TNOs, and found that the surfaces of TNOs can be well described by two surface
classifications, BrightIR and FaintIR. These classifications both include
optically red members and are differentiated predominantly based on whether
their near-infrared spectral slope is similar to their optical spectral slope.
The vast majority of cold classical TNOs, with dynamically quiescent orbits,
have the FaintIR surface classification, and we infer that TNOs in other
dynamical classifications with FaintIR surfaces share a common origin with the
cold classical TNOs. Comparison between the resonant populations and the
possible parent populations of cold classical and dynamically excited TNOs
reveal that the 3:2 has minimal contributions from the FaintIR class, which
could be explained by the secular resonance clearing the region near
the 3:2 before any sweeping capture occurred. Conversely, the fraction of
FaintIR objects in the 4:3 resonance, 2:1 resonance, and the resonances within
the cold classical belt, suggest that the FaintIR surface formed in the
protoplanetary disk between 34.6 and 47 au, though the outer bound depends on
the degree of resonance sweeping during migration. The presence and absence of
the FaintIR surfaces in Neptune's resonances provides critical constraints for
the history of Neptune's migration, the evolution of the , and the
surface class distribution in the initial planetesimal diskComment: 19 pages, 8 figures. in Press at PS
The Debiased Compositional Distribution of MITHNEOS : Global Match between the Near-Earth and Main-belt Asteroid Populations, and Excess of D-type Near-Earth Objects
We report 491 new near-infrared spectroscopic measurements of 420 near-Earth objects (NEOs) collected on the NASA InfraRed Telescope Facility as part of the MIT-Hawaii NEO Spectroscopic Survey. These measurements were combined with previously published data from Binzel et al. and bias-corrected to derive the intrinsic compositional distribution of the overall NEO population, as well as of subpopulations coming from various escape routes (ERs) in the asteroid belt and beyond. The resulting distributions reflect well the overall compositional gradient of the asteroid belt, with decreasing fractions of silicate-rich (S- and Q-type) bodies and increasing fractions of carbonaceous (B-, C-, D- and P-type) bodies as a function of increasing ER distance from the Sun. The close compositional match between NEOs and their predicted source populations validates dynamical models used to identify ERs and argues against any strong composition change with size in the asteroid belt between similar to 5 km and similar to 100 m. A notable exception comes from the overabundance of D-type NEOs from the 5:2J and, to a lesser extend, the 3:1J and nu (6) ERs, hinting at the presence of a large population of small D-type asteroids in the main belt. Alternatively, this excess may indicate preferential spectral evolution from D-type surfaces to C and P types as a consequence of space weathering, or point to the fact that D-type objects fragment more often than other spectral types in the NEO space. No further evidence for the existence of collisional families in the main belt, below the detection limit of current main-belt surveys, was found in this work.Peer reviewe
Col-OSSOS: Z-Band Photometry Reveals Three Distinct TNO Surface Types
Several different classes of trans-Neptunian objects (TNOs) have been
identified based on their optical and near-infrared colors. As part of the
Colours of the Outer Solar System Origins Survey, we have obtained , ,
and band photometry of 26 TNOs using Subaru and Gemini Observatories.
Previous color surveys have not utilized band reflectance, and the
inclusion of this band reveals significant surface reflectance variations
between sub-populations. The colors of TNOs in and show obvious
structure, and appear consistent with the previously measured bi-modality in
. The distribution of colors of the two dynamically excited surface types
can be modeled using the two-component mixing models from Fraser \& Brown
(2012). With the combination of and , the dynamically excited
classes can be separated cleanly into red and neutral surface classes. In and , the two dynamically excited surface groups are also clearly
distinct from the cold classical TNO surfaces, which are red, with
0.85 and 0.6, while all dynamically excited objects
with similar colors exhibit redder colors. The band photometry
makes it possible for the first time to differentiate the red excited TNO
surfaces from the red cold classical TNO surfaces. The discovery of different
colors for these cold classical TNOs makes it possible to search for cold
classical surfaces in other regions of the Kuiper belt and to completely
separate cold classical TNOs from the dynamically excited population, which
overlaps in orbital parameter space.Comment: 11 pages, 2 figures, Accepted to A
Spectral evolution of dark asteroid surfaces induced by space weathering over a decade
The surface of airless bodies like asteroids in the Solar System are known to
be affected by space weathering. Experiments simulating space weathering are
essential for studying the effects of this process on meteorite samples, but
the problem is that the time spent to reproduce space weathering in these
experiments is billions of times shorter than the actual phenomenon. In
December 2010, the T-type asteroid 596 Scheila underwent a collision with a
few-tens-of-meters impactor. A decade later, there is an opportunity to study
how the surface layer of this asteroid is being altered by space weathering
after the impact. To do so, we performed visible spectrophotometric and
near-infrared spectroscopic observations of 596 Scheila. The acquired spectrum
is consistent with those observed shortly after the 2010 impact event within
the observational uncertainty range. This indicates that the surface color of
dark asteroids is not noticeably changed by space weathering over a 10-year
period. This study is the first to investigate color changes due to space
weathering on an actual asteroid surface in the Solar System. Considering that
fresh layers are regularly created on asteroid surfaces by collisions, we
suggest a genetic link between D/T-type and dark (low albedo) X-complex
asteroids and very red objects such as 269 Justitia, 732 Tjilaki (and 203
Pompeja). New observations show that 203 Pompeja has a X-type-like surface,
with some local surface areas exhibiting a very red spectrum.Comment: 16 pages, 9 figures, 2 tables, Accepted for publication in ApJ
Letter
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