arXiv subjects

Katelyn Allers

Publications and source records attributed to Katelyn Allers.

25 records · Page 2Linked to original sources

arXiv2019

A 3 Gyr White Dwarf with Warm Dust Discovered via the Backyard Worlds: Planet 9 Citizen Science Project

Infrared excesses due to dusty disks have been observed orbiting white dwarfs with effective temperatures between 7200 K and 25000 K, suggesting that the rate of tidal disruption of minor bodies massive enough to create a coherent disk declines sharply beyond 1~Gyr after white dwarf formation. We report the discovery that the candidate white dwarf LSPM J0207+3331, via the Backyard Worlds: Planet 9 citizen science project and Keck Observatory follow-up spectroscopy, is hydrogen-dominated with a luminous compact disk (L$_{\rm IR}$/L$_{\star}$=14%) and an effective temperature nearly 1000K cooler than any known white dwarf with an infrared excess. The discovery of this object places the latest time for large scale tidal disruption events to occur at $\sim$3 Gyr past the formation of the host white dwarf, making new demands of dynamical models for planetesimal perturbation and disruption around post main sequence planetary systems. Curiously, the mid-IR photometry of the disk cannot be fully explained by a geometrically thin, optically thick dust disk as seen for other dusty white dwarfs, but requires a second ring of dust near the white dwarf's Roche radius. In the process of confirming this discovery, we found that careful measurements of WISE source positions can reveal when infrared excesses for white dwarfs are co-moving with their hosts, helping distinguish them from confusion noise.

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arXiv2018

Constraining the multiplicity statistics of the coolest brown dwarfs: binary fraction continues to decrease with spectral type

Binary statistics of the latest-type T and Y brown dwarfs are sparse and it is unclear whether the trends seen in the multiplicity properties of their more massive counterparts hold for the very coolest brown dwarfs. We present results from a search for substellar and planetary-mass companions to a sample of 12 ultracool T8$-$Y0 field brown dwarfs with the Hubble Space Telescope/Wide Field Camera 3. We find no evidence for resolved binary companions among our sample down to separations of 0.7$-$2.5 AU. Combining our survey with prior searches, we place some of the first statistically robust constraints to date on the multiplicity properties of the coolest, lowest-mass brown dwarfs in the field. Accounting for observational biases and incompleteness, we derive a binary frequency of $f = 5.5^{+5.2}_{-3.3}$% for T5$-$Y0 brown dwarfs at separations of 1.5$-$1000 AU, for an overall binary fraction of $f_\mathrm{tot} = 8\pm6$%. Modelling the projected separation as a lognormal distribution, we find a peak in separation at $ρ_0 = 2.9^{+0.8}_{-1.4}$ AU with a logarithmic width of $σ= 0.21^{+0.14}_{-0.08}$. We infer a mass ratio distribution peaking strongly towards unity, with a power law index of $γ= 6.1^{+4.0}_{-2.7}$, reinforcing the significance of the detection of a tighter and higher mass ratio companion population around lower-mass primaries. These results are consistent with prior studies and support the idea of a decreasing binary frequency with spectral type in the Galactic field.

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arXiv2017

Simultaneous, Multi-Wavelength Variability Characterization of the Free-Floating Planetary Mass Object PSO J318.5-22

We present simultaneous HST WFC3 + Spitzer IRAC variability monitoring for the highly-variable young ($\sim$20 Myr) planetary-mass object PSO J318.5-22. Our simultaneous HST + Spitzer observations covered $\sim$2 rotation periods with Spitzer and most of a rotation period with HST. We derive a period of 8.6$\pm$0.1 hours from the Spitzer lightcurve. Combining this period with the measured $v sin i$ for this object, we find an inclination of 56.2$\pm 8.1^{\circ}$. We measure peak-to-trough variability amplitudes of 3.4$\pm$0.1$\%$ for Spitzer Channel 2 and 4.4 - 5.8$\%$ (typical 68$\%$ confidence errors of $\sim$0.3$\%$) in the near-IR bands (1.07-1.67 $μ$m) covered by the WFC3 G141 prism -- the mid-IR variability amplitude for PSO J318.5-22 one of the highest variability amplitudes measured in the mid-IR for any brown dwarf or planetary mass object. Additionally, we detect phase offsets ranging from 200--210$^{\circ}$ (typical error of $\sim$4$^{\circ}$) between synthesized near-IR lightcurves and the Spitzer mid-IR lightcurve, likely indicating depth-dependent longitudinal atmospheric structure in this atmosphere. The detection of similar variability amplitudes in wide spectral bands relative to absorption features suggests that the driver of the variability may be inhomogeneous clouds (perhaps a patchy haze layer over thick clouds), as opposed to hot spots or compositional inhomogeneities at the top-of-atmosphere level.

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arXiv2016

The First Spectrum of the Coldest Brown Dwarf

The recently discovered brown dwarf WISE 0855 presents our first opportunity to directly study an object outside the Solar System that is nearly as cold as our own gas giant planets. However the traditional methodology for characterizing brown dwarfs---near infrared spectroscopy---is not currently feasible as WISE 0855 is too cold and faint. To characterize this frozen extrasolar world we obtained a 4.5-5.2 $μ$m spectrum, the same bandpass long used to study Jupiter's deep thermal emission. Our spectrum reveals the presence of atmospheric water vapor and clouds, with an absorption profile that is strikingly similar to Jupiter. The spectrum is high enough quality to allow the investigation of dynamical and chemical processes that have long been studied in Jupiter's atmosphere, but now on an extrasolar world.

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arXiv2015

Variability in a Young, L/T Transition Planetary-Mass Object

As part of our ongoing NTT SoFI survey for variability in young free-floating planets and low mass brown dwarfs, we detect significant variability in the young, free-floating planetary mass object PSO J318.5-22, likely due to rotational modulation of inhomogeneous cloud cover. A member of the 23$\pm$3 Myr $β$ Pic moving group, PSO J318.5-22 has T$_\mathrm{eff}$ = 1160$^{+30}_{-40}$ K and a mass estimate of 8.3$\pm$0.5 M$_{Jup}$ for a 23$\pm$3 Myr age. PSO J318.5-22 is intermediate in mass between 51 Eri b and $β$ Pic b, the two known exoplanet companions in the $β$ Pic moving group. With variability amplitudes from 7-10$\%$ in J$_{S}$ at two separate epochs over 3-5 hour observations, we constrain the rotational period of this object to $>$5 hours. In K$_{S}$, we marginally detect a variability trend of up to 3$\%$ over a 3 hour observation. This is the first detection of weather on an extrasolar planetary mass object. Among L dwarfs surveyed at high-photometric precision ($<$3$\%$) this is the highest amplitude variability detection. Given the low surface gravity of this object, the high amplitude preliminarily suggests that such objects may be more variable than their high mass counterparts, although observations of a larger sample is necessary to confirm this. Measuring similar variability for directly imaged planetary companions is possible with instruments such as SPHERE and GPI and will provide important constraints on formation. Measuring variability at multiple wavelengths can help constrain cloud structure.

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arXiv2011

A Keck LGS AO Search for Brown Dwarf and Planetary Mass Companions to Upper Scorpius Brown Dwarfs

We searched for binary companions to 20 young brown dwarfs in the Upper Scorpius association (145 pc, 5 Myr, nearest OB association) with the the Laser Guide Star adaptive optics system and the facility infrared camera NIRC2 on the 10 m Keck II telescope. We discovered a 0.14" companion (20.9+-0.4 AU) to the <0.1 MSun object SCH J16091837-20073523. From spectral deconvolution of integrated-light near-IR spectroscopy of SCH1609 using the SpeX spectrograph (Rayner et al. 2003), we estimate primary and secondary spectral types of M6+-0.5 and M7+-1.0, corresponding to masses of 79+-17 MJup and 55+-25 MJup at an age of 5 Myr and masses of 84+-15 MJup and 60+-25 MJup at an age of 10 Myr. For our survey objects with spectral types later than M8, we find an upper limit on the binary fraction of <9% (1-sigma) at separations of 10 -- 500 AU. We combine the results of our survey with previous surveys of Upper Sco and similar young regions to set the strongest constraints to date on binary fraction for young substellar objects and very low mass stars. The binary fraction for low mass (<40 MJup) brown dwarfs in Upper Sco is similar to that for T dwarfs in the field; for higher mass brown dwarfs and very low mass stars, there is an excess of medium-separation (10-50 AU projected separation) young binaries with respect to the field. These medium separation binaries will likely survive to late ages.

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arXiv2010

A Spitzer Search For Planetary-Mass Brown Dwarfs With Circumstellar Disks: Candidate Selection

We report on initial results from a Spitzer program to search for very low-mass brown dwarfs in Ophiuchus. This program is an extension of an earlier study by Allers et al. which had resulted in an extraordinary success rate, 18 confirmed out of 19 candidates. Their program combined near-infrared and Spitzer photom- etry to identify objects with very cool photospheres together with circumstellar disk emission to indicate youth. Our new program has obtained deep IRAC pho- tometry of a 0.5 deg2 field that was part of the original Allers et al. study. We report 18 new candidates whose luminosities extend down to 10-4 L\cdot which sug- gests masses down to ~ 2 MJ if confirmed. We describe our selection techniques, likely contamination issues, and follow-on photometry and spectroscopy that are in progress.

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