arXiv subjects

Daniella C. Bardalez Gagliuffi

Publications and source records attributed to Daniella C. Bardalez Gagliuffi.

At least 55 records · Page 3Linked to original sources

arXiv2021

Calibration of the Halpha Age-Activity relation for M dwarfs

In this work, we calibrate the relationship between Halpha emission and M dwarf ages. We compile a sample of 892 M dwarfs with Halpha equivalent width (HaEW) measurements from the literature that are either co-moving with a white dwarf of known age (21 stars) or in a known young association (871 stars). In this sample we identify 7 M dwarfs that are new candidate members of known associations. By dividing the stars into active and inactive categories according to their HaEW and spectral type (SpT), we find that the fraction of active dwarfs decreases with increasing age, and the form of the decline depends on SpT. Using the compiled sample of age-calibrators we find that HaEW and fractional Halpha luminosity (LHaLbol) decrease with increasing age. HaEW for SpT<M7 decreases gradually up until ~1Gyr. For older ages, we found only two early M dwarfs which are both inactive and seem to continue the gradual decrease. We also found 14 mid-type out of which 11 are inactive and present a significant decrease of HaEW, suggesting that the magnetic activity decreases rapidly after ~1Gyr. We fit LHaLbol versus age with a broken power-law and find an index of -0.11+0.02-0.01 for ages <~776Myr. The index becomes much steeper at older ages however a lack of field age-calibrators leaves this part of the relation far less constrained. Finally, from repeated independent measurements for the same stars we find that 94% of these has a level of HaEW variability <=5A at young ages (<1Gyr).

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arXiv2020

The Y dwarf population with HST: unlocking the secrets of our coolest neighbours -- I. Overview & First astrometric results

In this paper we present our project that aims at determining accurate distances and proper motions for the Y brown dwarf population using the Hubble Space Telescope. We validate the program with our first results, using a single new epoch of observations of the Y0pec dwarf WISE J163940.83$-$684738.6. These new data allowed us to refine its proper motion and improve the accuracy of its parallax by a factor of three compared to previous determinations, now constrained to $\varpi = 211.11 \pm 0.56$ mas. This newly derived absolute parallax corresponds to a distance of $4.737 \pm 0.013$ pc, an exquisite and unprecedented precision for faint ultracool Y dwarfs.

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arXiv2020

The Field Substellar Mass Function Based on the Full-sky 20-pc Census of 525 L, T, and Y Dwarfs

We present final Spitzer trigonometric parallaxes for 361 L, T, and Y dwarfs. We combine these with prior studies to build a list of 525 known L, T, and Y dwarfs within 20 pc of the Sun, 38 of which are presented here for the first time. Using published photometry and spectroscopy as well as our own follow-up, we present an array of color-magnitude and color-color diagrams to further characterize census members, and we provide polynomial fits to the bulk trends. Using these characterizations, we assign each object a $T_{\rm eff}$ value and judge sample completeness over bins of $T_{\rm eff}$ and spectral type. Except for types $\ge$ T8 and $T_{\rm eff} <$ 600K, our census is statistically complete to the 20-pc limit. We compare our measured space densities to simulated density distributions and find that the best fit is a power law ($dN/dM \propto M^{-α}$) with $α= 0.6{\pm}0.1$. We find that the evolutionary models of Saumon & Marley correctly predict the observed magnitude of the space density spike seen at 1200K $< T_{\rm eff} <$ 1350K, believed to be caused by an increase in the cooling timescale across the L/T transition. Defining the low-mass terminus using this sample requires a more statistically robust and complete sample of dwarfs $\ge$Y0.5 and with $T_{\rm eff} <$ 400K. We conclude that such frigid objects must exist in substantial numbers, despite the fact that few have so far been identified, and we discuss possible reasons why they have largely eluded detection.

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arXiv2020

Individual Dynamical Masses of DENIS J063001.4$-$184014AB Reveal A Likely Young Brown Dwarf Triple

The binary nature of the M8.5 dwarf DENIS J063001.4$-$184014AB (DE0630$-$18) was discovered with astrometric monitoring from the ground, which determined the unresolved photocentric orbit and the trigonometric parallax of the system. Here we present radial-velocity monitoring and resolved observations in the near-infrared with Keck aperture masking that allow us to measure the system's relative separation and brightness. By combining all available information, we determine the individual dynamical masses of the binary components to be $M_1 = 0.052^{+0.009}_{-0.008} M_\mathrm{Sun}$ and $M_2 = 0.052^{+0.005}_{-0.004} M_\mathrm{Sun}$, both firmly in the substellar regime. These masses are surprising given the object's M8.5 optical spectral type and equivalent absolute magnitude, and the significant difference in brightness between the components ($Δ{K}$ = 1.74$\pm$0.06 mag). Our results suggest that DE0630$-$18 is a relatively young system ($\sim$200 Myr) with a secondary component that is itself a potentially unresolved binary.

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arXiv2020

A Dynamical Mass of $70 \pm 5$ Jupiter Masses for Gliese 229B, the First T Dwarf

We combine Keck/HIRES radial velocities, imaging with HiCIAO/Subaru and the Hubble Space Telescope, and absolute astrometry from Hipparcos and Gaia to measure a dynamical mass of $70 \pm 5$ Jupiter masses for the brown dwarf companion to Gl 229. Gl 229B was the first imaged brown dwarf to show clear signs of methane in its atmosphere. Cooling models have been used to estimate a mass in the range of 20 - 55 Jupiter masses, much lower than our measured value. We argue that our high dynamical mass is unlikely to be due to perturbations from additional unseen companions or to Gl 229B being itself a binary, and we find no evidence of a previously claimed radial velocity planet around Gl 229A. Future Gaia data releases will confirm the reliability of the absolute astrometry, though the data pass all quality checks in both Hipparcos and Gaia. Our dynamical mass implies a very old age for Gl 229, in some tension with kinematic and activity age indicators, and/or shortcomings in brown dwarf cooling models. Gl 229B joins a small but growing list of T dwarfs with masses approaching the minimum mass for core hydrogen ignition.

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arXiv2020

Spitzer Follow-up of Extremely Cold Brown Dwarfs Discovered by the Backyard Worlds: Planet 9 Citizen Science Project

We present Spitzer follow-up imaging of 95 candidate extremely cold brown dwarfs discovered by the Backyard Worlds: Planet 9 citizen science project, which uses visually perceived motion in multi-epoch WISE images to identify previously unrecognized substellar neighbors to the Sun. We measure Spitzer [3.6]-[4.5] color to phototype our brown dwarf candidates, with an emphasis on pinpointing the coldest and closest Y dwarfs within our sample. The combination of WISE and Spitzer astrometry provides quantitative confirmation of the transverse motion of 75 of our discoveries. Nine of our motion-confirmed objects have best-fit linear motions larger than 1"/yr; our fastest-moving discovery is WISEA J155349.96+693355.2 (total motion ~2.15"/yr), a possible T type subdwarf. We also report a newly discovered wide-separation (~400 AU) T8 comoving companion to the white dwarf LSPM J0055+5948 (the fourth such system to be found), plus a candidate late T companion to the white dwarf LSR J0002+6357 at 5.5' projected separation (~8,700 AU if associated). Among our motion-confirmed targets, five have Spitzer colors most consistent with spectral type Y. Four of these five have exceptionally red Spitzer colors suggesting types of Y1 or later, adding considerably to the small sample of known objects in this especially valuable low-temperature regime. Our Y dwarf candidates begin bridging the gap between the bulk of the Y dwarf population and the coldest known brown dwarf.

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arXiv2020

WISEA J083011.95+283716.0: A Missing Link Planetary-Mass Object

We present the discovery of WISEA J083011.95+283716.0, the first Y dwarf candidate identified through the Backyard Worlds: Planet 9 citizen science project. We identified this object as a red, fast-moving source with a faint $W2$ detection in multi-epoch \textit{AllWISE} and unWISE images. We have characterized this object with Spitzer Space Telescope and \textit{Hubble Space Telescope} follow-up imaging. With mid-infrared detections in \textit{Spitzer}'s \emph{ch1} and \emph{ch2} bands and flux upper limits in Hubble Space Telescope $F105W$ and $F125W$ filters, we find that this object is both very faint and has extremely red colors ($ch1-ch2 = 3.25\pm0.23$ mag, $F125W-ch2 \geq 9.36$ mag), consistent with a T$_{eff}\sim300$ K source, as estimated from the known Y dwarf population. A preliminary parallax provides a distance of $11.1^{+2.0}_{-1.5}$ pc, leading to a slightly warmer temperature of $\sim350$ K. The extreme faintness and red Hubble Space Telescope and Spitzer Space Telescope colors of this object suggest it may be a link between the broader Y dwarf population and the coldest known brown dwarf WISE J0855$-$0714, and highlight our limited knowledge of the true spread of Y dwarf colors. We also present four additional Backyard Worlds: Planet 9 late-T brown dwarf discoveries within 30 pc.

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arXiv2019

WISE2150-7520AB: A very low mass, wide co-moving brown dwarf system discovered through the citizen science project Backyard Worlds: Planet 9

We report the discovery of WISE2150-7520AB (W2150AB): a widely separated (~ 341 AU) very low mass L1 + T8 co-moving system. The system consists of the previously known L1 primary 2MASS J21501592-7520367 and a newly discovered T8 secondary found at position 21:50:18.99 -75:20:54.6 (MJD=57947) using Wide-field Infrared Survey Explorer (WISE) data via the Backyard Worlds: Planet 9 citizen science project. We present Spitzer ch1 and ch2 photometry (ch1-ch2= 1.41 +/-0.04 mag) of the secondary and FIRE prism spectra of both components. The sources show no peculiar spectral or photometric signatures indicating that each component is likely field age. Using all observed data and the Gaia DR2 parallax of 41.3593 +/- 0.2799 mas for W2150A we deduce fundamental parameters of log(Lbol/Lsun)=-3.69 +/- 0.01, Teff=2118 +/- 62 K, and an estimated mass=72 +/- 12 MJup for the L1 and log(Lbol/Lsun)=-5.64 +/- 0.02, Teff=719 +/- 61 K, and an estimated mass=34 +/- 22 MJup for the T8. At a physical separation of ~341 AU this system has Ebin = 10^41 erg making it the lowest binding energy system of any pair with Mtot < 0.1 Msun not associated with a young cluster. It is equivalent in estimated mass ratio, Ebin, and physical separation to the ~ 2 Myr M7.25 + M8.25 binary brown dwarf 2MASS J11011926-7732383AB (2M1101AB) found in the Chameleon star forming region. W2150AB is the widest companion system yet observed in the field where the primary is an L dwarf or later.

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arXiv2019

The Ultracool SpeXtroscopic Survey. I. Volume-Limited Spectroscopic Sample and Luminosity Function of M7$-$L5 Ultracool Dwarfs

We present a volume-limited, spectroscopically-verified sample of M7$-$L5 ultracool dwarfs within 25\,pc. The sample contains 410 sources, of which $93\%$ have trigonometric distance measurements ($80\%$ from \textit{Gaia} DR2), and $81\%$ have low-resolution ($R\sim120$), near-infrared (NIR) spectroscopy. We also present an additional list of 60 sources which may be M7$-$L5 dwarfs within 25\,pc when distance or spectral type uncertainties are taken into account. The spectra provide NIR spectral and gravity classifications, and we use these to identify young sources, red and blue $J-K_S$ color outliers, and spectral binaries. We measure very low gravity and intermediate gravity fractions of $2.1^{+0.9}_{-0.8}\%$ and $7.8^{+1.7}_{-1.5}\%$, respectively; fractions of red and blue color outliers of $1.4^{+0.6}_{-0.5}$\% and $3.6^{+1.0}_{-0.9}$\%, respectively; and a spectral binary fraction of $1.6^{+0.5}_{-0.5}\%$. We present an updated luminosity function for M7$-$L5 dwarfs continuous across the hydrogen burning limit that agrees with previous studies. We estimate our completeness to range between $69-80\%$ when compared to an isotropic model. However, we find that the literature late-M sample is severely incomplete compared to L dwarfs, with completeness of $62^{+8}_{-7}\%$ and $83^{+10}_{-9}\%$, respectively. This incompleteness can be addressed with astrometric-based searches of ultracool dwarfs with \textit{Gaia} to identify objects previously missed by color- and magnitude-limited surveys.

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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.

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arXiv2018

2MASS J13243553+6358281 is an Early T-Type Planetary-Mass Object in the AB Doradus Moving Group

We present new radial velocity and trigonometric parallax measurements indicating that the unusually red and photometrically variable T2 dwarf 2MASS J13243553+6358281 is a member of the young (~150 Myr) AB Doradus moving group based on its space velocity. We estimate its model-dependent mass in the range 11-12 $M_{\rm Jup}$ at the age of the AB Doradus moving group, and its trigonometric parallax distance of 12.7 $\pm$ 1.5 pc makes it one of the nearest known isolated planetary-mass objects. The unusually red continuum of 2MASS J13243553+6358281 in the near-infrared was previously suspected to be caused by an unresolved L+T brown dwarf binary, although it was never observed with high-spatial resolution imaging. This new evidence of youth suggests that a low surface gravity may be sufficient to explain this peculiar feature. Using the new parallax we find that its absolute $J$-band magnitude is ~0.4 mag fainter than equivalent-type field brown dwarfs, suggesting that the binary hypothesis is unlikely. The fundamental properties of 2MASS J13243553+6358281 follow the spectral type sequence of other known high-likelihood members of the AB Doradus moving group. The effective temperature of 2MASS J13243553+6358281 provides the first precise constraint on the L/T transition at a known young age, and indicates that it happens at a temperature of ~1150 K at ~150 Myr, compared to ~1250 K for field brown dwarfs.

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arXiv2018

An L+T Spectral Binary with Possible AB Doradus Kinematics

We present the identification of WISE~J135501.90$-$825838.9 as a spectral binary system with a slight possibility of planetary-mass components in the $130-200$\,Myr AB~Doradus moving group. Peculiarities in the near-infrared spectrum of this source suggest it to be a blended-light binary with L6.0$\pm$1.0 and T3.0$\pm$1.8 or L7.0$\pm$0.6 and T7.5$\pm$0.4 components. Its proper motion and radial velocity as a combined-light source yield a high membership probability for AB~Doradus. While the young L6+T3 case is underluminous in a color-magnitude diagram at the AB~Doradus kinematic distance, the young L7+T7.5 case could be viable. Gravity-sensitive indicators are more consistent with a field-age binary. If confirmed as a young object, member of AB~Doradus, we estimate masses of 11$\pm$1\,\mjup\ and 9$\pm$1\,\mjup\ with both component masses below the Deuterium burning mass limit. Otherwise, we find masses of $72^{+4}_{-5}$ and $61^{+6}_{-8}$ for the field L6+T3 case and $70^{+2}_{-4}$ and $42^{+5}_{-6}$ for the field L7+T7.5 case. Our identification of WISE~J135501.90$-$825838.9 as a candidate young spectral binary introduces a new technique for detecting and characterizing planetary-mass companions to young brown dwarfs.

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arXiv2017

2MASS J11151597+1937266: A Young, Dusty, Isolated, Planetary-Mass Object with a Potential Wide Stellar Companion

We present 2MASS J11151597+1937266, a recently identified low-surface gravity L dwarf, classified as an L2$γ$ based on Sloan Digital Sky Survey optical spectroscopy. We confirm this spectral type with near-infrared spectroscopy, which provides further evidence that 2MASS J11151597+1937266 is a low-surface gravity L dwarf. This object also shows significant excess mid-infrared flux, indicative of circumstellar material; and its strong H$α$ emission (EW$_{\mathrm{H}α}=560\pm82$ Å) is an indicator of enhanced magnetic activity or weak accretion. Comparison of its spectral energy distribution to model photospheres yields an effective temperature of $1724^{+184}_{-38}$ K. We also provide a revised distance estimate of $37\pm6$ pc using a spectral type-luminosity relationship for low-surface gravity objects. The 3-dimensional galactic velocities and positions of 2MASS J11151597+1937266 do not match any known young association or moving group. Assuming a probable age in the range of 5-45 Myr, the model-dependent estimated mass of this object is between 7-21 $M_\mathrm{Jup}$, making it a potentially isolated planetary-mass object. We also identify a candidate co-moving, young stellar companion, 2MASS J11131089+2110086.

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arXiv2017

Identification of WISE J000100.45+065259.6 as an M8.5+T5 Spectral Binary Candidate

[not part of RNAAS note] We report the discovery of WISE J000100.45+065259.6 as a very low mass star/brown dwarf spectral binary candidate, on the basis of low resolution near-infrared spectroscopy obtained with IRTF/SpeX. Decomposition of the spectrum indicates component types of M8.5+T5 with a predicted $Δ{J}$ = 3.5. As the majority of confirmed spectral binary candidates to date are very closely-separated systems ($ρ$ $\lesssim$ 3 AU; $P$ $\lesssim$ 15~yr), this source may provide mass measurements across the hydrogen burning limit within the decade.

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arXiv2016

A Brown Dwarf Census from the SIMP Survey

We have conducted a near-infrared (NIR) proper motion survey, the Sondage Infrarouge de Mouvement Propre, in order to discover field ultracool dwarfs (UCD) in the solar neighborhood. The survey was conducted by imaging $\sim28\%$ of the sky with the Caméra PAnoramique Proche-InfraRouge both in the southern hemisphere at the Cerro Tololo Inter-American Observatory 1.5 m telescope, and in the northern hemisphere at the Observatoire du Mont-Mégantic 1.6 m telescope and comparing the source positions from these observations with the Two Micron All-Sky Survey Point Source Catalog (2MASS PSC). Additional color criteria were used to further discriminate unwanted astrophysical sources. We present the results of an NIR spectroscopic follow-up of 169 M, L, and T dwarfs. Among the sources discovered are 2 young field brown dwarfs, 6 unusually red M and L dwarfs, 25 unusually blue M and L dwarfs, 2 candidate unresolved L+T binaries, and 24 peculiar UCDs. Additionally, we add 9 L/T transition dwarfs (L6--T4.5) to the already known objects.

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arXiv2015

High Resolution Imaging of Very Low Mass Spectral Binaries: Three Resolved Systems and Detection of Orbital Motion in an L/T Transition Binary

We present high resolution Laser Guide Star Adaptive Optics imaging of 43 late-M, L and T dwarf systems with Keck/NIRC2. These include 17 spectral binary candidates, systems whose spectra suggest the presence of a T dwarf secondary. We resolve three systems: 2MASS J1341$-$3052, SDSS J1511+0607 and SDSS J2052$-$1609; the first two are resolved for the first time. All three have projected separations $<8$ AU and estimated periods of $14-80$ years. We also report a preliminary orbit determination for SDSS J2052$-$1609 based on six epochs of resolved astrometry between 2005$-$2010. Among the 14 unresolved spectral binaries, 5 systems were confirmed binaries but remained unresolved, implying a minimum binary fraction of $47^{+12}_{-11}\%$ for this sample. Our inability to resolve most of the spectral binaries, including the confirmed binaries, supports the hypothesis that a large fraction of very low mass systems have relatively small separations and are missed with direct imaging.

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arXiv2015

Results from the Wide-field Infrared Survey Explorer (WISE) Future Uses Session at the WISE at 5 Meeting

During the "WISE at 5: Legacy and Prospects" conference in Pasadena, CA -- which ran from February 10 - 12, 2015 -- attendees were invited to engage in an interactive session exploring the future uses of the Wide-field Infrared Survey Explorer (WISE) data. The 65 participants -- many of whom are extensive users of the data -- brainstormed the top questions still to be answered by the mission, as well as the complementary current and future datasets and additional processing of WISE/NEOWISE data that would aid in addressing these most important scientific questions. The results were mainly bifurcated between topics related to extragalactic studies (e.g. AGN, QSOs) and substellar mass objects. In summary, participants found that complementing WISE/NEOWISE data with cross-correlated multiwavelength surveys (e.g. SDSS, Pan-STARRS, LSST, Gaia, Euclid, etc.) would be highly beneficial for all future mission goals. Moreover, developing or implementing machine-learning tools to comb through and understand cross-correlated data was often mentioned for future uses. Finally, attendees agreed that additional processing of the data such as co-adding WISE and NEOWISE and extracting a multi-epoch photometric database and parallax and proper motion catalog would greatly improve the scientific results of the most important projects identified. In that respect, a project such as MaxWISE which would execute the most important additional processing and extraction as well as make the data and catalogs easily accessible via a public portal was deemed extremely important.

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arXiv2014

SpeX Spectroscopy of Unresolved Very Low Mass Binaries. II. Identification of Fourteen Candidate Binaries with Late-M/Early-L and T Dwarf Components

Multiplicity is a key statistic for understanding the formation of very low mass (VLM) stars and brown dwarfs. Currently, the separation distribution of VLM binaries remains poorly constrained at small separations ($\leq$ 1 AU), leading to uncertainty in the overall binary fraction. We approach this problem by searching for late-M/early-L plus T dwarf spectral binaries whose combined light spectra exhibit distinct peculiarities, allowing for separation-independent identification. We define a set of spectral indices designed to identify these systems, and use a spectral template fitting method to confirm and characterize spectral binary (SB) candidates from a library of 815 spectra from the SpeX Prism Spectral Libraries. We present eleven new binary candidates, confirm three previously reported candidates and rule out two previously identified candidates, all with primary and secondary spectral types between M7-L7 and T1-T8, respectively. We find that subdwarfs and blue L dwarfs are the primary contaminants in our sample and propose a method for segregating these sources. If confirmed by follow-up observations, these systems may add to the growing list of tight separation binaries, whose orbital properties may yield further insight into brown dwarf formation scenarios.

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