arXiv subjects

Federico Marocco

Publications and source records attributed to Federico Marocco.

47 records · Page 3Linked to original sources

arXiv2020

Characterization of the Nucleus, Morphology and Activity of Interstellar Comet 2I/Borisov by Optical and Near-Infrared GROWTH, Apache Point, IRTF, ZTF and Keck Observations

We present visible and near-infrared photometric and spectroscopic observations of interstellar object 2I/Borisov taken from 2019 September 10 to 2019 November 29 using the GROWTH, the APO ARC 3.5 m and the NASA/IRTF 3.0 m combined with post and pre-discovery observations of 2I obtained by ZTF from 2019 March 17 to 2019 May 5. Comparison with imaging of distant Solar System comets shows an object very similar to mildly active Solar System comets with an out-gassing rate of $\sim$10$^{27}$ mol/sec. The photometry, taken in filters spanning the visible and NIR range shows a gradual brightening trend of $\sim0.03$ mags/day since 2019 September 10 UTC for a reddish object becoming neutral in the NIR. The lightcurve from recent and pre-discovery data reveals a brightness trend suggesting the recent onset of significant H$_2$O sublimation with the comet being active with super volatiles such as CO at heliocentric distances $>$6 au consistent with its extended morphology. Using the advanced capability to significantly reduce the scattered light from the coma enabled by high-resolution NIR images from Keck adaptive optics taken on 2019 October 04, we estimate a diameter of 2I's nucleus of $\lesssim$1.4 km. We use the size estimates of 1I/'Oumuamua and 2I/Borisov to roughly estimate the slope of the ISO size-distribution resulting in a slope of $\sim$3.4$\pm$1.2, similar to Solar System comets and bodies produced from collisional equilibrium.

astro-ph.EP↗

arXiv2020

The CatWISE Preliminary Catalog: Motions from ${\it WISE}$ and ${\it NEOWISE}$ Data

CatWISE is a program to catalog sources selected from combined ${\it WISE}$ and ${\it NEOWISE}$ all-sky survey data at 3.4 and 4.6 $μ$m (W1 and W2). The CatWISE Preliminary Catalog consists of 900,849,014 sources measured in data collected from 2010 to 2016. This dataset represents four times as many exposures and spans over ten times as large a time baseline as that used for the AllWISE Catalog. CatWISE adapts AllWISE software to measure the sources in coadded images created from six-month subsets of these data, each representing one coverage of the inertial sky, or epoch. The catalog includes the measured motion of sources in 8 epochs over the 6.5 year span of the data. From comparison to ${\it Spitzer}$, the SNR=5 limits in magnitudes in the Vega system are W1=17.67 and W2=16.47, compared to W1=16.96 and W2=16.02 for AllWISE. From comparison to ${\it Gaia}$, CatWISE positions have typical accuracies of 50 mas for stars at W1=10 mag and 275 mas for stars at W1=15.5 mag. Proper motions have typical accuracies of 10 mas yr$^{-1}$ and 30 mas yr$^{-1}$ for stars with these brightnesses, an order of magnitude better than from AllWISE. The catalog is available in the WISE/NEOWISE Enhanced and Contributed Products area of the NASA/IPAC Infrared Science Archive.

astro-ph.IM↗

arXiv2019

Improved infrared photometry and a preliminary parallax measurement for the extremely cold brown dwarf CWISEP J144606.62$-$231717.8

We present follow-up $Spitzer$ observations at 3.6$μ$m (ch1) and 4.5$μ$m (ch2) of CWISEP J144606.62$-$231717.8, one of the coldest known brown dwarfs in the solar neighborhood. This object was found by mining the Wide-field Infrared Survey Explorer ($WISE$) and $NEOWISE$ data via the CatWISE Preliminary Catalog by Meisner et al. (2019b), where an initial $Spitzer$ color of ch1$-$ch2 = 3.71$\pm$0.44 mag was reported, implying it could be one of the reddest, and hence coldest, known brown dwarfs. Additional $Spitzer$ data presented here allows us to revise its color to ch1$-$ch2 = 2.986$\pm$0.048 mag, which makes CWISEP J144606.62$-$231717.8 the 5th reddest brown dwarf ever observed. A preliminary trigonometric parallax measurement, based on a combination of $WISE$ and $Spitzer$ astrometry, places this object at a distance of 10.1$^{+1.7}_{-1.3}$ pc. Based on our improved $Spitzer$ color and preliminary parallax, CWISEP J144606.62$-$231717.8 has a $T_{\rm eff}$ in the 310$-$360 K range. Assuming an age of 0.5$-$13 Gyr, this corresponds to a mass between 2 and 20 $M_{\rm Jup}$.

astro-ph.SR↗

arXiv2019

Expanding the Y Dwarf Census with Spitzer Follow-up of the Coldest CatWISE Solar Neighborhood Discoveries

We present Spitzer 3.6$μ$m and 4.5$μ$m follow-up of 170 candidate extremely cool brown dwarfs newly discovered via the combination of WISE and NEOWISE imaging at 3$-$5$μ$m. CatWISE, a joint analysis of archival WISE and NEOWISE data, has improved upon the motion measurements of AllWISE by leveraging a $>$10$\times$ time baseline enhancement, from 0.5 years (AllWISE) to 6.5 years (CatWISE). As a result, CatWISE motion selection has yielded a large sample of previously unrecognized brown dwarf candidates, many of which have archival detections exclusively in the WISE 4.6$μ$m (W2) channel, suggesting that they could be both exceptionally cold and nearby. Where these objects go undetected in WISE W1 (3.4$μ$m), Spitzer can provide critically informative detections at 3.6$μ$m. Of our motion-confirmed discoveries, seventeen have a best-fit Spitzer [3.6]$-$[4.5] color most consistent with spectral type Y. CWISEP J144606.62$-$231717.8 ($μ\approx 1.3''$/yr) is likely the reddest, and therefore potentially coldest, member of our sample with a very uncertain [3.6]$-$[4.5] color of 3.71 $\pm$ 0.44 magnitudes. We also highlight our highest proper motion discovery, WISEA J153429.75$-$104303.3, with $μ\approx 2.7''$/yr. Given that the prior list of confirmed and presumed Y dwarfs consists of just 27 objects, the Spitzer follow-up presented in this work has substantially expanded the sample of identified Y dwarfs. Our new discoveries thus represent significant progress toward understanding the bottom of the substellar mass function, investigating the diversity of the Y dwarf population, and selecting optimal brown dwarf targets for JWST spectroscopy.

astro-ph.SR↗

arXiv2019

CWISEP J193518.59$-$154620.3: An Extremely Cold Brown Dwarf in the Solar Neighborhood Discovered with CatWISE

We present the discovery of an extremely cold, nearby brown dwarf in the solar neighborhood, found in the CatWISE catalog (Eisenhardt et al., in prep.). Photometric follow-up with Spitzer reveals that the object, CWISEP J193518.59-154620.3, has ch1$-$ch2 = 3.24$\,\pm\,$0.31 mag, making it one of the reddest brown dwarfs known. Using the Spitzer photometry and the polynomial relations from Kirkpatrick et al. (2019) we estimate an effective temperature in the $\sim$270--360 K range, and a distance estimate in the 5.6$-$10.9 pc range. We combined the WISE, NEOWISE, and Spitzer data to measure a proper motion of $μ_α\cos δ= 337\pm69$ mas yr$^{-1}$, $μ_δ= -50\pm97$ mas yr$^{-1}$, which implies a relatively low tangential velocity in the range 7$-$22 km s$^{-1}$.

astro-ph.SR↗

arXiv2019

Substellar Multiplicity Throughout the Ages

Substellar multiplicity is a key outcome of the formation process. The biggest challenge for the next decade will be to distinguish between the formation history, environmental conditions, and dynamical evolution leading to the least massive brown dwarfs and the most massive planets at the tail ends of their mass functions. In this white paper, we advocate for a comprehensive characterization of both the statistical distributions of the population of ultracool dwarf multiple systems and the fundamental properties of their individual components as a function of age. A space-based precision astrometry mission in near-infrared wavelengths would provide the necessary measurements to identify and characterize age-calibrated populations of multiple systems.

astro-ph.SR↗

arXiv2018

Preliminary Trigonometric Parallaxes of 184 Late-T and Y Dwarfs and an Analysis of the Field Substellar Mass Function into the "Planetary" Mass Regime

We present preliminary trigonometric parallaxes of 184 late-T and Y dwarfs using observations from Spitzer (143), USNO (18), NTT (14), and UKIRT (9). To complete the 20-pc census of $\ge$T6 dwarfs, we combine these measurements with previously published trigonometric parallaxes for an additional 44 objects and spectrophotometric distance estimates for another 7. For these 235 objects, we estimate temperatures, sift into five 150K-wide $T_{\rm eff}$ bins covering the range 300-1050K, determine the completeness limit for each, and compute space densities. To anchor the high-mass end of the brown dwarf mass spectrum, we compile a list of early- to mid-L dwarfs within 20 pc. We run simulations using various functional forms of the mass function passed through two different sets of evolutionary code to compute predicted distributions in $T_{\rm eff}$. The best fit of these predictions to our L, T, and Y observations is a simple power-law model with $α\approx 0.6$ (where $dN/dM \propto M^{-α}$), meaning that the slope of the field substellar mass function is in rough agreement with that found for brown dwarfs in nearby star forming regions and young clusters. Furthermore, we find that published versions of the log-normal form do not predict the steady rise seen in the space densities from 1050K to 350K. We also find that the low-mass cutoff to formation, if one exists, is lower than $\sim$5 $M_{Jup}$, which corroborates findings in young, nearby moving groups and implies that extremely low-mass objects have been forming over the lifetime of the Milky Way.

astro-ph.SR↗

arXiv2018

A Late-type L Dwarf at 11 pc Hiding in the Galactic Plane Characterized Using Gaia DR2

We report on the characterization of a nearby (d = 11.2 pc) ultracool L dwarf (WISE J192512.78+070038.8; hereafter W1925) identified as a faint (G = 20.0) high proper motion (0.22"/yr) object in the Gaia Data Releases 1 and 2. A Palomar/TripleSpec near-infrared spectrum of W1925 confirms a previously estimated photometric L7 spectral type by Scholz et al. 2018, and its infrared colors and absolute magnitudes are consistent with a single object of this type. We constructed a spectral energy distribution using the Gaia parallax, literature photometry and near infrared spectrum and find a luminosity log(Lbol/LSun) = -4.443+/-0.008. Applying evolutionary models, we infer that W1925 is likely a 53+/-18 MJup brown dwarf with Teff=1404+/-71 K and log g =5.1+/-0.4 dex (cgs). While W1925 was detected in both the 2MASS and WISE infrared sky surveys, it was not detected in photographic plate sky surveys. Its combination of extreme optical-infrared colors, high proper motion, and location near the crowded Galactic plane (b = -4.2 deg) likely contributed to it having evaded detection in pre-Gaia surveys.

astro-ph.SR↗

arXiv2014

WISEP J061135.13-041024.0AB: A J-Band Flux Reversal Binary at the L/T Transition

We present Keck II laser guide star adaptive optics observations of the brown dwarf WISEP J061135.13-041024.0 showing it is a binary with a component separation of 0.4". This system is one of the six known resolved binaries in which the magnitude differences between the components show a reversal in sign between the Y/J band and the H/K bands. Deconvolution of the composite spectrum results in a best fit binary solution with L9 and T1.5 components. We also present a preliminary parallax placing the system at a distance of 21.2+/-1.3 pc. Using the distance and resolved magnitudes we are able to place WISEP J061135.13-041024.0AB on a color-absolute magnitude diagram, showing that this system contributes to the well-known "J-band bump" and the components' properties appear similar to other late-type L and early-type T dwarfs. Fitting our data to a set of cloudy atmosphere models suggests the system has an age >1 Gyr with WISEP J061135.13-041024.0A having an effective temperature (Teff) of 1275-1325 K and mass of 64-65 M_Jup, and WISEP J061135.13-041024.0B having Teff = 1075-1115 K and mass 40-65 M_Jup.

astro-ph.SR↗

arXiv2013

The Kinematic Age of the Coolest T Dwarfs

Surprisingly, current atmospheric models suggest that the coolest T dwarfs (T8.5 to T10) are young and very low mass (0.06-2Gyr, 5-20Mjup, Leggett et al.2009, 2010, 2012). Studies of population kinematics offer an independent constraint on the age of the population. We present kinematic data of a sample of 75 mid to late T dwarfs drawn from a variety of sources. We define our samples, T5.5 to T8 and T8.5 to T10, as mid and late T respectively. UKIDSS LAS kinematics were derived from our automated LAS proper motion pipeline and distance estimates derived from spectral types and photometry for the minority of sources that lack parallaxes. Our results show that the mid and late T populations do not have distinctly separate tangential velocity distributions to 95% probability. They also give an approximate mean kinematic age equal to that of a population with B-V colour 0.51-0.54, and a spectral type late F, which corresponds to an age of about 2 Gyr. However the median and modal ages are greater. This indicates that while model atmospheres correctly predict some trends in colour with gravity and age, reliable ages cannot yet be inferred from them. More benchmark objects are needed to anchor the models.

astro-ph.SR↗

arXiv2010

The discovery of a very cool, very nearby brown dwarf in the Galactic plane

We report the discovery of a very cool, isolated brown dwarf, UGPS 0722-05, with the UKIDSS Galactic Plane Survey. The near-infrared spectrum displays deeper H2O and CH4 troughs than the coolest known T dwarfs and an unidentified absorption feature at 1.275 um. We provisionally classify the object as a T10 dwarf but note that it may in future come to be regarded as the first example of a new spectral type. The distance is measured by trigonometric parallax as d=4.1{-0.5}{+0.6} pc, making it the closest known isolated brown dwarf. With the aid of Spitzer/IRAC we measure H-[4.5] = 4.71. It is the coolest brown dwarf presently known -- the only known T dwarf that is redder in H-[4.5] is the peculiar T7.5 dwarf SDSS J1416+13B, which is thought to be warmer and more luminous than UGPS 0722-05. Our measurement of the luminosity, aided by Gemini/T-ReCS N band photometry, is L = 9.2 +/- 3.1x10^{-7} Lsun. Using a comparison with well studied T8.5 and T9 dwarfs we deduce Teff=520 +/- 40 K. This is supported by predictions of the Saumon & Marley models. With apparent magnitude J=16.52, UGPS 0722-05 is the brightest T dwarf discovered by UKIDSS so far. It offers opportunities for future study via high resolution near-infrared spectroscopy and spectroscopy in the thermal infrared.

astro-ph.SR↗