Partial Light Curves Research Articles

The DECam Ecliptic Exploration Project (DEEP). IV. Constraints on the Shape Distribution of Bright Trans-Neptunian Objects

We present the methods and results from the discovery and photometric measurement of 26 bright VR > 24 trans-Neptunian objects (TNOs) during the first year (2019–20) of the DECam Ecliptic Exploration Project (DEEP). The DEEP survey is an observational TNO survey with wide sky coverage, high sensitivity, and a fast photometric cadence. We apply a computer vision technique known as a progressive probabilistic Hough transform to identify linearly moving transient sources within DEEP photometric catalogs. After subsequent visual vetting, we provide a photometric and astrometric catalog of our TNOs. By modeling the partial lightcurve amplitude distribution of the DEEP TNOs using Monte Carlo techniques, we find our data to be most consistent with an average TNO axis ratio b/a < 0.5, implying a population dominated by non-spherical objects. Based on ellipsoidal gravitational stability arguments, we find our data to be consistent with a TNO population containing a high fraction of contact binaries or other extremely non-spherical objects. We also discuss our data as evidence that the expected binarity fraction of TNOs may be size-dependent.

Deep learning unresolved lensed light curves

ABSTRACT Gravitationally lensed sources may have unresolved or blended multiple images, and for time varying sources, the light curves from individual images can overlap. We use convolutional neural nets to both classify the light curves as due to unlensed, double, or quad lensed sources and fit for the time delays. Focusing on lensed supernova systems with time delays Δt ≳ 6 d, we achieve 100 per cent precision and recall in identifying the number of images and then estimating the time delays to σΔt ≈ 1 d, with a 1000× speedup relative to our previous Monte Carlo technique. This also succeeds for flux noise levels $\sim 10{{\ \rm per\ cent}}$. For Δt ∈ [2, 6] d, we obtain 94–98 per cent accuracy, depending on image configuration. We also explore using partial light curves where observations only start near maximum light, without the rise time data, and quantify the success.

Asteroid Photometry from the Transiting Exoplanet Survey Satellite: A Pilot Study

Abstract The Transiting Exoplanet Survey Satellite (TESS) searches for planets transiting bright and nearby stars using high-cadence, large-scale photometric observations. Full frame images provided by the TESS mission include a large number of serendipitously observed main-belt asteroids (MBAs). Due to the cadence of the published full frame images, we are sensitive to periods as long as of order tens of days, a region of phase space that is generally not accessible through traditional observing. This work represents a much less biased measurement of the period distribution in this period range. We have derived rotation periods for 300 MBAs and have partial lightcurves for a further 7277 asteroids, including 43 with periods of P &gt; 100 hr; this large number of slow rotators is predicted by theory. Of these slow rotators we find none requiring significant internal strength to resist rotational reshaping. We find our derived rotation periods to be in excellent agreement with results in the Lightcurve Database for the 55 targets that overlap. Over the nominal two-year lifetime of the mission, we expect the detection of around 85,000 unique asteroids with rotation period solutions for around 6000 asteroids. We project that the systematic analysis of the entire TESS data set will increase the number of known slow-rotating asteroids (period &gt; 100 hr) by a factor of 10. Comparing our new period determinations with previous measurements in the literature, we find that the rotation period of asteroid (2320) Blarney has decreased by at least 20% over the past decade, potentially due to surface activity or subcatastrophic collisions.

OSSOS. XII. Variability Studies of 65 Trans-Neptunian Objects Using the Hyper Suprime-Cam

We present variability measurements and partial light curves of Trans-Neptunian Objects (TNOs) from a two-night pilot study using Hyper Suprime-Cam (HSC) on the Subaru Telescope (Maunakea, Hawai'i, USA). Subaru's large aperture (8-m) and HSC's large field of view (1.77 square degrees) allow us to obtain measurements of multiple objects with a range of magnitudes in each telescope pointing. We observed 65 objects with m_r = 22.6--25.5 mag in just six pointings, allowing 20--24 visits of each pointing over the two nights. Our sample, all discovered in the recent Outer Solar System Origins Survey (OSSOS), span absolute magnitudes H_r = 6.2--10.8 mag and thus investigates smaller objects than previous light curve projects have typically studied. Our data supports the existence of a correlation between light curve amplitude and absolute magnitude seen in other works, but does not support a correlation between amplitude and orbital inclination. Our sample includes a number of objects from different dynamical populations within the trans-Neptunian region, but we do not find any relationship between variability and dynamical class. We were only able to estimate periods for 12 objects in the sample and found that a longer baseline of observations is required for reliable period analysis. We find that 31 objects (just under half of our sample) have variability greater than 0.4 magnitudes during all of the observations; in smaller 1.25 hr, 1.85 hr and 2.45 hr windows, the median variability is 0.13, 0.16 and 0.19 mags, respectively. The fact that variability on this scale is common for small TNOs has important implications for discovery surveys (such as OSSOS or the Large Synoptic Survey Telescope) and color measurements.

Constraining the Shape Distribution of Near-Earth Objects from Partial Light Curves

Abstract In the absence of dense photometry for a large population of near-Earth objects (NEOs), the best method of obtaining a shape distribution comes from sparse photometry and partial light curves. We have used 867 partial light curves obtained by Spitzer to determine a shape distribution for subkilometer NEOs. From this data we find a best-fit average elongation of . We compare this result with a shape distribution obtained from 1869 NEOs in the same size range observed by Pan-STARRS 1 (PS1) and find the Spitzer-obtained elongation to be in excellent agreement with this PS1 value of . These values are also in agreement with literature values for 1 &lt; D &lt; 10 km objects in the main asteroid belt, however, there is a size discrepancy between the two data sets. Using a smaller sample of NEOs in the size range of 1 &lt; D &lt; 5 km from PS1 data, we obtain an average axis ratio of b/a = 0.70 ± 0.12. This is more elongated than the shape distribution for main belt objects in the same size regime, although the current uncertainties are sizeable and this should be verified using a larger data set. As future large surveys come online it will be possible to observe smaller main belt asteroids to allow for better comparisons of different subkilometer populations.

The Plutino Population: An Abundance of Contact Binaries

Abstract We observed 12 Plutinos over two separated years with the 4.3 m Lowell’s Discovery Channel Telescope. Here, we present the first light-curve data for those objects. Three of them (2014 JL80, 2014 JO80, and 2014 JQ80) display a large light-curve amplitude explainable by a single elongated object, but they are most likely caused by a contact binary system due to their light-curve morphology. These potential contact binaries have rotational periods from 6.3 to 34.9 hr and peak-to-peak light-curve variability between 0.6 and 0.8 mag. We present partial light curves, allowing us to constrain the light-curve amplitude and the rotational period of another nine Plutinos. By merging our data with the literature, we estimate that up to ∼40% of the Plutinos could be contact binaries. Interestingly, we found that all of the suspected contact binaries in the 3:2 resonance are small with absolute magnitude H &gt; 6 mag. Based on our sample and the literature, up to ∼50% of the small Plutinos are potential contact binaries.

On the Rotation Period and Shape of the Hyperbolic Asteroid 1I/‘Oumuamua (2017 U1) from Its Lightcurve

Abstract We observed the newly discovered hyperbolic minor planet 1I/‘Oumuamua (2017 U1) on 2017 October 30 with Lowell Observatory’s 4.3 m Discovery Channel Telescope. From these observations, we derived a partial lightcurve with a peak-to-trough amplitude of at least 1.2 mag. This lightcurve segment rules out rotation periods less than 3 hr and suggests that the period is at least 5 hr. On the assumption that the variability is due to a changing cross-section, the axial ratio is at least 3:1. We saw no evidence for a coma or tail in either individual images or in a stacked image having an equivalent exposure time of 9000 s.

WASP-42 b and WASP-49 b: two new transiting sub-Jupiters

We report the discovery of two new transiting planets from the WASP survey. WASP-42 b is a 0.500 +/- 0.035 M_jup planet orbiting a K1 star at a separation of 0.0548 +/- 0.0017 AU with a period of 4.9816872 +/- 7.3 x 10^-6 days. The radius of WASP-42 b is 1.080 +/- 0.057 R_jup while its equilibrium temperature is T_eq = 995 +/- 34 K. We detect some evidence for a small but non-zero eccentricity of e=0.060 +/- 0.013. WASP-49 b is a 0.378 +/- 0.027 M_jup planet around an old G6 star. It has a period of 2.7817387 +/- 5.6 x 10^-6 days and a separation of 0.0379 +/- 0.0011 AU. This planet is slightly bloated, having a radius of 1.115 +/- 0.047 R_jup and an equilibrium temperature of T_eq = 1369 +/- 39 K. Both planets have been followed up photometrically, and in total we have obtained 5 full and one partial transit light curves of WASP-42 and 4 full and one partial light curves of WASP-49 using the Euler-Swiss, TRAPPIST and Faulkes South telescopes.

WASP-36b: A NEW TRANSITING PLANET AROUND A METAL-POOR G-DWARF, AND AN INVESTIGATION INTO ANALYSES BASED ON A SINGLE TRANSIT LIGHT CURVE

We report the discovery, from WASP and CORALIE, of a transiting exoplanet in a 1.54-d orbit. The host star, WASP-36, is a magnitude V = 12.7, metal-poor G2 dwarf (Teff = 5959 \pm 134 K), with [Fe/H] = -0.26 \pm 0.10. We determine the planet to have mass and radius respectively 2.30 \pm 0.07 and 1.28 \pm 0.03 times that of Jupiter. We have eight partial or complete transit light curves, from four different observatories, which allows us to investigate the potential effects on the fitted system parameters of using only a single light curve. We find that the solutions obtained by analysing each of these light curves independently are consistent with our global fit to all the data, despite the apparent presence of correlated noise in at least two of the light curves.

GROUND-BASED MULTISITE OBSERVATIONS OF TWO TRANSITS OF HD 80606b

We present ground-based optical observations of the September 2009 and January 2010 transits of HD 80606b. Based on 3 partial light curves of the September 2009 event, we derive a midtransit time of T_c [HJD] = 2455099.196 +- 0.026, which is about 1 sigma away from the previously predicted time. We observed the January 2010 event from 9 different locations, with most phases of the transit being observed by at least 3 different teams. We determine a midtransit time of T_c [HJD] = 2455210.6502 +- 0.0064, which is within 1.3 sigma of the time derived from a Spitzer observation of the same event.

Thermal rotational lightcurve of dwarf-planet (1) Ceres at 235 GHz with the Submillimeter Array

Context. Previously published measurements of the millimeter-wave thermal rotational lightcurve of dwarf-planet (1) Ceres show incompatible results, proposing peak-to-peak lightcurve amplitudes during the ∼9 h rotation period of either 4% or 50%, the latter being difficult to explain physically. Aims. Better calibrated measurements are necessary to firmly assess the behavior of Ceres’ thermal lightcurve, and to relate possible brightness temperature variations to the distribution of local surface properties such as bolometric albedo and emissivity. Methods. One partial lightcurve of 6.5 h was obtained with the Submillimeter Array (Hawaii) in subcompact configuration at 235 GHz in January 2009, providing better absolute and relative calibration than the previously used single-dish facilities. Results. The observed disk-averaged lightcurve is compatible with no variation over the measurement window, and has an upper limit of 3% on its amplitude. Conclusions. The results obtained rule out the possibility of extreme brightness temperature variations, and the upper limit on the lightcurve amplitude could be physically realized by a combination of albedo distribution and realistic ground emissivity variations.

Determination of stellar, orbital and planetary parameters using complete Monte-Carlo analysis – the case of HAT-P-7b

AbstractThe recently discovered transiting very hot Jupiter, HAT-P-7b, a planet detected by the telescopes of HATNet, turned out to be among the ones subjected to the highest irradiation from the parent star. In order to best characterize this particular planet, we carried out an analysis based on a complete and simultaneous Monte-Carlo solution using all available data. We included the discovery light curves, partial follow-up light curves, the radial velocity data, and we used the stellar evolution models to infer the stellar properties.This self-consistent way of modeling provides the most precise estimate of the a posteriori distributions of all of the system parameters of interest, and avoids making assumptions on the values and uncertainties of any of the internally derived variables describing the system. This analysis demonstrates that even partial light curve information can be valuable. This may become very important for future discoveries of planets with longer periods – and therefore longer transit durations – where the chance of observing a full event is small.

Hubble Space Telescope observations of the nucleus of Comet 9P/Tempel 1

The nucleus of Comet 9P/Tempel 1, the target of the Deep Impact mission, was detected during Hubble Space Telescope observations taken with the wide-field planetary camera 2 (WFPC2) on 31 December 1997 when the comet's solar phase angle was 3 . ° 8 , its heliocentric distance was 4.48 AU, and its geocentric distance was 3.53 AU. Sixteen images were taken through the F675W filter, and all of them revealed a point-like source without any detectable coma. From these images, we derived the R magnitude of the nucleus in the Johnson–Kron–Cousins photometric system for the entire 11.5-h time span of the observations. Assuming a prolate spheroid whose spin axis lies close to the plane of the sky, the partial lightcurve indicates semi-axes a − 3.9 km and b − 2.8 km (assuming a geometric albedo of 0.04 for the R band and a phase coefficient of 0.04 mag deg −1) and a rotational period in the range of ∼ 25 − 33 h . The upper limit of the parameter Afρ, which characterizes the dust production rate, is 1 cm. We also derive a fractional active area at 1.78 AU of ∼ 4 % .

Four new binary minor planets: (854) Frostia, (1089) Tama, (1313) Berna, (4492) Debussy

Context.

Archival light curves from the Bamberg Sky Patrol: CF Octantis, 1964-76

We use the archive of the Bamberg Sky Patrol to obtain light curves of the active K subgiant CF Octantis (HD 196818) for the interval 1964–76. Digitized images of the field near CF Oct were obtained with a flat-bed scanner. Aperture photometry was performed of photo-positives of these images. Using a transformation to second order in plate magnitude, and first order in B−V, for nine field stars for each plate, the B magnitudes of CF Oct were obtained for just over 350 plates. The estimated precision of an individual determination of the B magnitude of CF Oct is 0.05 mag. Analysis of the resulting data reveals the known 20 d rotational variation of this star, and shows the evolution of the light curves from year to year. We obtain light curves with good phase coverage for 1964 to 1969 inclusive, partial light curves for 1970 and 1976, and a few data points from 1971. The amplitude of variation ranges from ∼0.2 to ∼0.4 mag. There is evidence that the characteristic rotation period of the star in the 1960s was slightly less than that measured from photoelectric photometry in the 1980s.

TNO Recovery, Unlocking the Early Solar System

The recent discoveries of small bodies in the outer solar system in the vicinity of the Kuiper belt are revolutionizing solar system formation concepts by providing critical dynamical and compositional clues to its earliest epochs. However, the rapidly accelerating discovery rate means that follow-up observations for orbit determination cannot keep up. We report here on an innovative test program to assess the potential of a small (2-m class) educational outreach telescope to engage in an efficient recovery program. Recovery observations have been obtained over the course of 22 nights using the University of Hawaii 2.2m telescope during 9 observing runs. We targeted over 200 objects and have achieved a 75% success rate. We obtained time resolved resolved light curve photometry on 2000 OK67, and the partial light curve suggests a period T &gt; 12 hr.

Hubble Space Telescope Observations of the Nucleus of Comet 9P/Tempel 1

The nucleus of Comet 9P/Tempel 1, the target of the Deep Impact mission, was detected during Hubble Space Telescope observations taken with the wide-field planetary camera 2 (WFPC2) on 31 December 1997 when the comet's solar phase angle was 3.°8, its heliocentric distance was 4.48 AU, and its geocentric distance was 3.53 AU. Sixteen images were taken through the F675W filter, and all of them revealed a point-like source without any detectable coma. From these images, we derived the R magnitude of the nucleus in the Johnson–Kron–Cousins photometric system for the entire 11.5-h time span of the observations. Assuming a prolate spheroid whose spin axis lies close to the plane of the sky, the partial lightcurve indicates semi-axes a=3.9 km and b=2.8 km (assuming a geometric albedo of 0.04 for the R band and a phase coefficient of 0.04 mag deg −1) and a rotational period in the range of ∼25–33 h. The upper limit of the parameter Afρ, which characterizes the dust production rate, is 1 cm. We also derive a fractional active area at 1.78 AU of ∼4%.

CCD Photometry of 2060 Chiron in 1985 and 1991

We report CCD photometry of 2060 Chiron from two apparitions. A partial light curve was obtained in 1985 January, when the object was intrinsically fainter ( H v = 6.84) than it has ever been seen before or since. Nonetheless, there was some evidence for cometary activity even then; the bare nucleus may be fainter still. A complete light curve was obtained over 10 hr on 1991 January 08. Similar in character to the 1990 lightcurve of J. X. Luu and D.C. Jewitt (1990, Astron. J. 100, 913-932), it differed in three important respects. The amplitude was lower (0.04 mag), the mean brightness level was higher than recent trends would predict (mean H R = 5.65), and the mean remained constant over 1 1 2 rotations to within better than 0.005 mag. The light curve shows reproducible structure of relatively high-frequency (∼15-min time scale), formerly attributed to noise. These features repeat within the night and also may be discerned in light curves dating back to 1986 (S. J. Bus, E. Bowell, A. W. Harris, and A. V. Hewitt, 1989, Icarus 77, 223-238). We believe this structure to be evidence that Chiron is more aspherical (faceted?) than the small-amplitude lightcurve otherwise implies. The rotational lightcurve now is sufficiently well-characterized that it is no longer necessary to obtain data over a complete rotation to monitor the so-called "outburst" behavior of the object. We hope that this will encourage observers to study the cometary behavior of Chiron on time scales of days to weeks. An updated mean synodic period of 5.917813 ± 0.000007 hr has been derived, and a revised nucleus + coma photometric model is constructed using the new data. The results of this model, along with the observed rapid "dropouts" in the rotational lightcurve, are together taken as evidence for a relatively low-obliquity viewing geometry over the past decade.

Photometric geodesy of main-belt asteroids: III. Additional lightcurves

We present observations of asteroids obtained in the period 1982–1989, comprising 107 complete or partial lightcurves of 59 different objects. These include additional data on “Photometric Geodesy” program asteroids (Weidenschilling et al. 1987, Icarus 70, 191–245), obtained to determine their shapes and pole orientations (Drummond et al. 1988, Icarus 76, 19–77), and targets of opportunity observed during the course of that program. We derive new or refined rotation periods for 16 asteroids, and estimates of, or constraints on, periods for 8 more. Data presented here and in Paper I (Weidenschilling et al. 1987) suggest that unusual lightcurves with unequal maxima and minima at large amplitudes are seen preferentially for M-type asteroids.

Rotation properties of four L5 Trojan asteroids from CCD photometry

CCD observations made with the Cerro Tololo 0.9-m telescope of four L5 Trojan asteroids during June and July of 1986 are presented. Partial lightcurves for 1208 Troilus and 1867 Deiphobus suggest long periods ( P > 24 hr). Complete lightcurves were obtained for two asteroids, 1173 Anchises ( P = 11.6095 ± 0.0036 hr, Δm = 0.57 ± 0.01 mag) and 2674 Pandarus ( P = 8.4803 ± 0.0019, Δm = 0.58 ± 0.01). The large lightcurve amplitudes are unique: from a sample of 182 main-belt asteroids, A. W. Harris and J. A. Burns (1979, Icarus 40, 115–144) found none in a comparable size range (50–100 km) with amplitudes greater than 0.5 mag. We suggest that the Trojans may represent a primordial asteroid population, with shapes not significantly altered since the formation of the solar system. Sufficient phase angle coverage was attained for 1173 Anchises to determine a near-opposition phase coefficient. No opposition effect was observed. The two-parameter function of E. Bowell, A. W. Harris, and K. Lumme (1985, preprint) and a linear phase coefficient both fit the data well. However, the multiple scattering parameter derived from the Bowell et al. model implies a geometric albedo of near unity, in conflict with the low radiometric albedos observed for Anchises and other Trojans ( D. P. Cruikshank, 1977, Icarus 30, 224–230). The lack of an opposition effect implies that the surface of Anchises may be significantly less rough than other asteroid suface