arXiv subjects

Annalisa Calamida

Publications and source records attributed to Annalisa Calamida.

At least 19 recordsLinked to original sources

arXiv2026

Probing the IMF in the Early Universe -- Direct measurements in the Bo\"otes I UFD with JWST/NIRCam

The dependence of the stellar initial mass function (IMF) on star-formation environment, particularly at low metallicities and high redshifts, remains poorly constrained. Ultra-faint dwarf galaxies (UFDs) are local fossils of high-redshift galaxies hosting old, metal-poor populations, and their resolved stellar populations provide unique pathways to constrain the sub-solar IMF. We investigate the low-mass IMF in the Bo{\"o}tes I (Boo I) UFD with JWST/NIRCam, leveraging its capability to resolve over 10,000 stars reaching $\lesssim$0.15\msun, obtaining one of the largest, deepest resolved stellar samples for UFDs. We explore three different functional forms of the IMF with machine learning and statistical techniques, combining forward modeling of synthetic color-magnitude diagrams with simulation-based inference. We find that a single power-law IMF provides a poorer description of the observed luminosity function and yields a slope inconsistent with the canonical Salpeter IMF. Our best-fit broken power-law and lognormal IMF parameters are consistent with the Milky Way within 68\% confidence level, providing evidence that star formation at metallicities as low as $\mathrm{[Fe/H]}\approx-2.4$ follows a similar IMF as in the Milky Way. By treating Boo I as a local relic analogous to a high-redshift galaxy with a stellar mass of $\lesssim10^5\msun$ at $z\gtrsim6$, our results provide evidence for the universality of the IMF across both local and high-redshift environments.

astro-ph.GA↗

arXiv2026

Attaining Spectral Energy Distributions With Sub-Percent Uncertainties: All-Sky DA White Dwarf Spectrophotometric Standard Stars For Large Telescopes And Surveys

We present a synopsis of the project to establish thirty-two new faint ($ 16.5 \leq V \leq 19.8 $) DA white dwarfs as spectrophotometric standards distributed over the whole sky. Our results validate the use of fully radiative pure hydrogen model fluxes for hot DA white dwarfs to predict the observed broadband fluxes from near ultraviolet through the near infrared to accuracies of a few parts per thousand. After fitting the line of sight reddenings simultaneously with the model spectral energy distributions of these stars against spectroscopic and multi-band photometric observations, we have shown that residuals have an rms of typically 0.4 percent. This indicates that the complications from interstellar dust extinction have been adequately mitigated. Our stars supplement the three brighter DA white dwarfs that define the flux scale of CALSPEC. The consequent photometric accuracy, their all sky coverage, and their brightness range that matches the dynamic range of large telescopes, constitutes an unprecedented ensemble of standard stars for both ground as well as space based use. This paper targets readers who may wish to use these as standard stars, and provides for them the essential content to understand their strengths and limitations, without traversing the technical details of analysis that are already captured in a series of papers since 2016. The narrative here describes the motivation, justification, and evolution of the analysis methods; the input data that constrain the modeling; as well as the stability of our results in the face of future improvements in models.

astro-ph.IM↗

arXiv2026

New Time-Dependent WFC3/IR Inverse Sensitivities

We present new time-dependent inverse sensitivities for the WFC3/IR channel. These were calculated using the sensitivity change slopes measured by \citet{2024wfc..rept....6M} and photometry of five CALSPEC standards (the white dwarfs GRW+70~5824, GD~153, GD~71, G191B2B, and the G-type star P330E) collected from 2009 to 2023. The new inverse sensitivities account for losses of 1-2\% over 15 years, depending on wavelength, and provide an internal photometric precision better than 0.5\% for all wide--, medium--, and narrow-band filters. An updated version of \texttt{calwf3} (v3.7.2) has been developed for use with a new time-dependent image photometry table (IMPHTTAB) and will be used to update the image header photometric keywords following MAST reprocessing, expected in late-2024. Alternatively, the new inverse sensitivities may be computed by the user for a specific observation date by running \texttt{stsynphot}.

astro-ph.IM↗

arXiv2026

WFC3/UVIS Geometric Distortion -- Time Evolution of Linear Terms w.r.t Gaia

We align more than 7,400 WFC3/UVIS exposures to the Gaia DR3 catalog to examine the time evolution of the linear terms (shift, rotation, scale and skew) of the geometric distortion solution between 2009 and 2022. We find small linear temporal changes in the scale and skew terms (less than 0.2 pixels in 13 years) which are generally dominated by intrinsic scatter (up to $\pm$ 0.3 pixels). Concurrently, a larger filter-dependent offset in the scale term is observed, with a maximum difference of 0.3 pixels between F275W and F814W images at all epochs. A small rotation offset to Gaia of 0.003 $\pm$ 0.004 degrees is measured from 2009 to mid-2017, after which the offsets are as large as 0.01 degrees, with a large scatter. MAST pipeline processing includes an additional alignment step which corrects UVIS images for any residual linear terms with respect to Gaia DR3 when there are at least 10 matched sources. In addition to any pointing offsets, this step accounts for any evolution in the distortion linear terms described here. For observers requiring high-precision astrometry, we recommend using the tweakreg routine to realign images using a 4-parameter fit (x-shift, y-shift, rotation, and scale) or a 6-parameter fit (x-shift, y-shift, x-rotation, y-rotation, x-scale, and y-scale) depending on the number of matched sources. We provide links to DrizzlePac tutorials for improving both absolute and relative astrometry in WFC3 images.

astro-ph.IM↗

arXiv2025

SKYSURF-11: A New Zodiacal Light Model Optimized for Optical Wavelengths

We present an improved zodiacal light model, optimized for optical wavelengths, using archival Hubble Space Telescope (HST) imaging from the SKYSURF program. The Kelsall et al. 1998 model used infrared imaging from the Diffuse Infrared Background Experiment (DIRBE) on board the Cosmic Background Explorer to create a 3D structure of the interplanetary dust cloud. However, this model cannot accurately represent zodiacal light emission outside of DIRBE's nominal wavelength bandpasses, the bluest of which is 1.25 micron. We present a revision to this model (called ZodiSURF) that incorporates analytical forms of both the scattering phase function and albedo as a function of wavelength, which are empirically determined across optical wavelengths (0.3-1.6 micron) from over 5,000 HST sky surface brightness (sky-SB) measurements. This refined model results in significantly improved predictions of zodiacal light emission at these wavelengths and for Sun angles greater than 80 deg. Fits to HST data show an uncertainty in the model of ~4.5%. Remarkably, the HST sky-SB measurements show an excess of residual diffuse light (HST Sky - ZodiSURF - Diffuse Galactic Light) of 0.013 +/- 0.006 MJy/sr. We suggest that a very dim spherical dust cloud may need to be included in the zodiacal light model, which we present here as a toy model.

astro-ph.CO↗

arXiv2025

An excess of luminous white dwarfs in the peculiar Galactic globular cluster NGC 2808

We study the white dwarf (WD) cooling sequence of the Galactic Globular Cluster (GGC) NGC 2808 by using deep near-UV data from the Hubble Space Telescope and theoretical models, to investigate if this cluster hosts an excess of WDs. Excess in WDs is a rare phenomenon that has been found to exist only in a few GGCs. We compared star counts from different evolutionary phases on the near-UV color-magnitude diagram to evolutionary times predicted by BaSTI models. The investigation was carried out over a region within a radii of 1.5 $\arcmin$ of the cluster center and a region of similar dimension located 5$\arcmin$ away. We find a WD excess of $\approx$ 60 - 70\% when comparing star counts and evolutionary models of the WD cooling sequence to the main-sequence turn-off, and by using different values and fractions of Helium enhancement. This excess decreases to $\approx$ 30 - 40\% when the WD cooling sequence is compared to the horizontal branch. The WD excess is slightly larger in the internal field that covers the cluster center; however, the difference with the external field is compatible within the uncertainties. We argue that this excess is possibly related to the existence of SCWDs and Helium-core WDs in NGC~2808, and might be directly associated to the extended blue horizontal branch of this GGC.

astro-ph.SR↗

arXiv2025

Wide binaries in an ultra-faint dwarf galaxy: discovery, population modeling, and a nail in the coffin of primordial black hole dark matter

We report the discovery and characterization of a wide binary population in the ultrafaint dwarf galaxy Boötes I using deep JWST/NIRCam imaging. Our sample consists of 52 candidate binaries with projected separations of 7,000 - 16,000 au and stellar masses from near the hydrogen-burning limit to the main-sequence turnoff ($\sim0.1$ - $0.8~{\rm M_\odot}$). By forward-modeling selection biases and chance alignments, we find that $1.25\pm0.25\%$ of Boötes I stars are members of wide binaries with separations beyond 5,000 au. This fraction, along with the distributions of separations and mass ratios, matches that in the Solar neighborhood, suggesting that wide binary formation is largely insensitive to metallicity, even down to [Fe/H] $\approx -2.5$. The observed truncation in the separation distribution near 16,000 au is well explained by stellar flyby disruptions. We also discuss how the binaries can be used to constrain the galaxy's dark matter properties. We show that our detection places new limits on primordial black hole dark matter, finding that compact objects with $M \gtrsim 5~{\rm M_\odot}$ cannot constitute more than $\sim1\%$ of the dark matter content. In contrast to previous work, we find that wide binaries are unlikely to provide robust constraints on the dark matter profile of ultrafaint galaxies given the uncertainties in the initial binary population, flyby disruptions, and contamination from chance alignments. These findings represent the most robust detection of wide binaries in an external galaxy to date, opening a new avenue for studying binary star formation and survival in extreme environments.

astro-ph.GA↗

arXiv2025

Betelgeuse's Buddy: X-Ray Constraints on the Nature of $α$ Ori B

The $\sim$$2100$d Long Secondary Period of Betelgeuse's optical lightcurve and radial velocity motivated the prediction of a low-mass stellar companion, expected to be at maximal apparent separation from Betelgeuse around December 2024. We carried out Director's Discretionary Time observations with the Chandra X-ray Observatory to identify any X-ray emission from the companion and constrain its nature as either a compact object or young stellar object (YSO). Past X-ray observations occurred at the wrong phase of the companion's orbit for optimal detection prospects and/or lacked the deep exposure required to constrain the typical X-ray luminosities of YSOs. In our 41.85 ks exposure with Chandra, we do not detect an X-ray source at the position of Betelgeuse. For an estimated hydrogen column density $N_H$$=$$6\times10^{22}$ cm$^{-2}$, we place a limit on the X-ray luminosity of $L_X$$\lesssim$$2\times10^{30}$ erg s$^{-1}$ ($\lesssim$$4.7\times10^{-4}L_\odot$) in $0.5$$-$$8$ keV for a 10 MK plasma temperature spectral model, or $L_X$$\lesssim$$5\times10^{29}$ erg s$^{-1}$ ($\lesssim$$1.2\times10^{-4}L_\odot$) for an absorbed power law with photon index $Γ$$=$$2$. These limits robustly exclude an accreting compact object (white dwarf or neutron star) as the companion. Solar mass YSOs with an age similar to Betelgeuse ($\sim$10 Myr) display a range of X-ray luminosities ($10^{28-32}$ erg s$^{-1}$), and we can place upper bounds within this range for most absorbing columns. Based on these considerations, we conclude that the companion to Betelgeuse is likely a low-mass YSO.

astro-ph.SR↗

arXiv2025

Betelgeuse, Betelgeuse, Betelgeuse, Betel-buddy? Constraints on the dynamical companion to $α$ Orionis from HST

Recently, two independent analyses have asserted that the cause of the Long Secondary Period (LSP) observed in the variability spectrum of our nearest red supergiant, Betelgeuse ($α$ Ori), is an as-yet undetected, low-mass binary companion dubbed $α$ Ori B. In this paper, we present the results of a far-UV observational campaign using the STIS echelle spectrograph on the Hubble Space Telescope aimed at detecting spectral signatures of the companion. The four-quadrant tiling pattern and timing of the observations were optimized to isolate the companion, with observations taking place during a period of maximum angular and velocity separation between Betelgeuse and the putative companion. Spectral differencing between quadrants recovers no spectral features at the companion's velocity in excess of the background or Betelgeuse's chromosphere, i.e. a non-detection. Having determined that $α$ Ori B is most likely a Young Stellar Object (YSO) thanks to constraints from a complementary X-ray campaign with the Chandra X-ray Observatory in a companion paper, comparison of our data against canonical spectra from YSOs in the ULLYSES database allows us to confidently exclude masses above $\gtrsim1.5M_\odot$ and companion continuum or line emission in excess of $\approx10^{-14}$ erg s$^{-1}$ cm$^{-2}$ angstrom$^{-1}$ in the FUV ($\approx1200-1700$ angstroms). Future observational campaigns aware of the LSP phase are needed to place deeper constraints on the spectroscopic nature of $α$ Ori B.

astro-ph.SR↗

arXiv2025

DAmodel: Hierarchical Bayesian Modelling of DA White Dwarfs for Spectrophotometric Calibration

We use hierarchical Bayesian modelling to calibrate a network of 32 all-sky faint DA white dwarf (DA WD) spectrophotometric standards ($16.5 < V < 19.5$) alongside three CALSPEC standards, from 912 Å to 32 $μ$m. The framework is the first of its kind to jointly infer photometric zeropoints and WD parameters (surface gravity $\log g$, effective temperature $T_{\text{eff}}$, extinction $A_V$, dust relation parameter $R_V$) by simultaneously modelling both photometric and spectroscopic data. We model panchromatic Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) UVIS and IR photometry, HST/STIS UV spectroscopy and ground-based optical spectroscopy to sub-percent precision. Photometric residuals for the sample are the lowest yet yielding $<0.004$ mag RMS on average from the UV to the NIR, achieved by jointly inferring time-dependent changes in system sensitivity and WFC3/IR count-rate nonlinearity. Our GPU-accelerated implementation enables efficient sampling via Hamiltonian Monte Carlo, critical for exploring the high-dimensional posterior space. The hierarchical nature of the model enables population analysis of intrinsic WD and dust parameters. Inferred spectral energy distributions from this model will be essential for calibrating the James Webb Space Telescope as well as next-generation surveys, including Vera Rubin Observatory's Legacy Survey of Space and Time and the Nancy Grace Roman Space Telescope.

astro-ph.IM↗

arXiv2025

OGLE-2011-BLG-0462: An Isolated Stellar-Mass Black Hole Confirmed Using New HST Astrometry and Updated Photometry

The long-duration Galactic-bulge microlensing event OGLE-2011-BLG-0462 produced relativistic astrometric deflections of the source star, which we measured using HST observations taken at 8 epochs over ~6 years. Analysis of the microlensing light curve and astrometry led our group (followed by other independent groups) to conclude that the lens is an isolated stellar-mass black hole (BH) -- the first and only one unambiguously discovered to date. There have now been three additional epochs of HST observations, increasing the astrometric time baseline to 11 years. Additionally, the ground-based OGLE data have been updated. We have re-analyzed the data, including the new HST astrometry, and photometry obtained with 16 different telescopes. The source lies only 0.4 arcsec from a bright neighbor, making it crucial to perform precise subtraction of its point-spread function (PSF) in the astrometric measurements of the source. Moreover, we show that it is essential to perform a separate PSF subtraction for each individual HST frame as part of the reductions. Our final solution yields a lens mass of 7.15 +/- 0.83 solar mass. Combined with the lack of detected light from the lens at late HST epochs, the BH nature of the lens is conclusively verified. The BH lies at a distance of 1.52 +/- 0.15 kpc, and is moving with a space velocity of 51.1 +/- 7.5 km/s relative to the stars in the neighborhood. We compare our results with those of other studies and discuss reasons for the differences. We searched for binary companions of the BH at a range of separations but found no evidence for any.

astro-ph.SR↗

arXiv2025

The dwarf irregular galaxy NGC 6822. II. Young, intermediate and old stellar populations: comparison between theory and observations

This paper presents a quantitative analysis of the stellar content in the Local Group dwarf irregular galaxy NGC 6822 by comparing stellar evolution models and observations in color-magnitude diagrams (CMDs) and color-color diagrams (CC-Ds). Our analysis is based on optical ground-based g,r,i photometry, and deep archive HST photometry of two fields in the galaxy disk. We compared young, intermediate-age, and old stellar populations with isochrones from the BaSTI-IAC library and found that NGC 6822 hosts a quite metal-rich ([Fe/H] = -0.7 to -0.4) young component with an age ranging from 20 to 100 Myr. The intermediate-age population experienced a modest chemical enrichment between 4 and 8 Gyr ago while stars older than 11 Gyr have a low metal abundance ([Fe/H] ~ -1.70). We also identified the AGB clump population with a luminosity peak at i ~ 23.35 mag. Our analysis of both the CMD and the optical-NIR-MIR CC-Ds of AGB oxygen- and carbon-rich stars, using the PARSEC+COLIBRI isochrones with and without circumstellar dust, reveal that this stellar component exhibits a spread in age from 1 to 2 Gyr and in metallicity between [Fe/H]=-1.30 and -1.70. The stellar models we used reproduce very well the two distinct color sequences defined by AGB O- and C-rich stars in the various optical-NIR-MIR CC-Ds, suggesting that they are reliable diagnostics to identify and characterise intermediate-age stellar populations. However, we also find that evolutionary prescriptions in the optical i-(r-i) CMDs predict, at fixed color, systematically lower luminosities than observed AGB stars.

astro-ph.GA↗

arXiv2024

Faint white dwarf flux standards: data and models

Fainter standard stars are essential for the calibration of larger telescopes. This work adds to the CALSPEC (calibration spectra) database 19 faint white dwarfs (WDs) with all-sky coverage and V magnitudes between 16.5 and 18.7. Included for these stars is new UV (ultraviolet) HST (Hubble Space Telescope) STIS (Space Telescope Imaging Spectrometer) spectrophotometry between 1150 and 3000~Å with a resolution of $\sim$500. Pure hydrogen WD models are fit to these UV spectra and to six-band HST/WFC3 (Wide Field Camera 3) photometry at 0.28 to 1.6~\micron\ to construct predicted model SEDs (spectral energy distributions) covering wavelengths from 900~Å to the JWST (James Webb Space Telescope) limit of 30~\micron\ using well-established CALSPEC procedures for producing flux standards with the goal of 1\% accuracy.

astro-ph.IM↗

arXiv2023

Extragalactic Star Cluster Science with the Nancy Grace Roman Space Telescope's High Latitude Wide Area Survey and the Vera C. Rubin Observatory

The Nancy Grace Roman Telescope's High Latitude Wide Area Survey will have a number of synergies with the Vera Rubin Observatory's Legacy Survey of Space and Time (LSST), particularly for extragalactic star clusters. Understanding the nature of star clusters and star cluster systems are key topics in many areas of astronomy, chief among them stellar evolution, high energy astrophysics, galaxy assembly/dark matter, the extragalactic distance scale, and cosmology. One of the challenges will be disentangling the age/metallicity degeneracy because young ($\sim$Myr) metal-rich clusters have similar SEDs to old ($\sim$Gyr) metal-poor clusters. Rubin will provide homogeneous, $ugrizy$ photometric coverage, and measurements in the red Roman filters will help break the age-metallicity and age-extinction degeneracies, providing the first globular cluster samples that cover wide areas while essentially free of contamination from Milky Way stars. Roman's excellent spatial resolution will also allow measurements of cluster sizes. We advocate for observations of a large sample of galaxies with a range of properties and morphologies in the Rubin/LSST footprint matching the depth of the LSST Wide-Fast-Deep field $i$ band limit (26.3 mag), and recommend adding the F213 filter to the survey.

astro-ph.GA↗

arXiv2023

All-Sky Faint DA White Dwarf Spectrophotometric Standards for Astrophysical Observatories: The Complete Sample

Hot DA white dwarfs have fully radiative pure hydrogen atmospheres that are the least complicated to model. Pulsationally stable, they are fully characterized by their effective temperature Teff, and surface gravity log g, which can be deduced from their optical spectra and used in model atmospheres to predict their spectral energy distribution (SED). Based on this, three bright DAWDs have defined the spectrophotometric flux scale of the CALSPEC system of HST. In this paper we add 32 new fainter (16.5 < V < 19.5) DAWDs spread over the whole sky and within the dynamic range of large telescopes. Using ground based spectra and panchromatic photometry with HST/WFC3, a new hierarchical analysis process demonstrates consistency between model and observed fluxes above the terrestrial atmosphere to < 0.004 mag rms from 2700 Å to 7750 Å and to 0.008 mag rms at 1.6μm for the total set of 35 DAWDs. These DAWDs are thus established as spectrophotometric standards with unprecedented accuracy from the near ultraviolet to the near-infrared, suitable for both ground and space based observatories. They are embedded in existing surveys like SDSS, PanSTARRS and GAIA, and will be naturally included in the LSST survey by Rubin Observatory. With additional data and analysis to extend the validity of their SEDs further into the IR, these spectrophotometric standard stars could be used for JWST, as well as for the Roman and Euclid observatories.

astro-ph.SR↗

arXiv2023

A Wide View of the Galactic Globular Cluster NGC 2808: Red Giant and Horizontal Branch Star Spatial Distributions

Wide-field and deep DECam multi-band photometry, combined with HST data for the core of the Galactic globular cluster NGC 2808, allowed us to study the distribution of various stellar sub-populations and stars in different evolutionary phases out to the cluster tidal radius. We used the C_ugi = (u-g)-(g-i) index to identify three chemically distinct sub-populations along the red giant branch and compared their spatial distributions. The most light-element enriched sub-population (P3) is more centrally concentrated; however, it shows a more extended distribution in the external regions of the cluster compared to the primordial (P1) and intermediate (P2) composition populations. Furthermore, the P3 sub-population centroid is off-center relative to those of the P1 and P2 groups. We also analyzed the spatial distribution of horizontal branch stars and found that the relative fraction of red horizontal branch stars increases for radial distances larger than ~ 1.5' while that of the blue and hotter stars decreases. These new observations, combined with literature spectroscopic measurements, suggest that the red horizontal branch stars are the progeny of all the stellar sub-populations in NGC 2808, i.e. primordial and light-element enhanced, while the blue stars are possibly the result of a combination of the "hot-flasher" and the "helium-enhanced" scenarios. A similar distribution of different red giant branch sub-populations and horizontal branch stars was also found for the most massive Galactic globular cluster, omega Cen, based on combined DECam and HST data, which suggests the two may share a similar origin.

astro-ph.GA↗

arXiv2023

SKYSURF-4: Panchromatic HST All-Sky Surface-Brightness Measurement Methods and Results

The diffuse, unresolved sky provides most of the photons that the Hubble Space Telescope (HST) receives, yet remains poorly understood. HST Archival Legacy program SKYSURF aims to measure the 0.2-1.6 $μ$m sky surface brightness (sky-SB) from over 140,000 HST images. We describe a sky-SB measurement algorithm designed for SKYSURF that is able to recover the input sky-SB from simulated images to within 1% uncertainty. We present our sky-SB measurements estimated using this algorithm on the entire SKYSURF database. Comparing our sky-SB spectral energy distribution (SED) to measurements from the literature shows general agreements. Our SKYSURF SED also reveals a possible dependence on Sun angle, indicating either non-isotropic scattering of solar photons off interplanetary dust or an additional component to Zodiacal Light. Finally, we update Diffuse Light limits in the near-IR based on the methods from Carleton et al. (2022), with values of 0.009 MJy sr$^{-1}$ (22 nW m$^{-2}$ sr$^{-1}$) at 1.25 $μ$m, 0.015 MJy sr$^{-1}$ (32 nW m$^{-2}$ sr$^{-1}$) at 1.4 $μ$m, and 0.013 MJy sr$^{-1}$ (25 nW m$^{-2}$ sr$^{-1}$) at 1.6 $μ$m. These estimates provide the most stringent all-sky constraints to date in this wavelength range. SKYSURF sky-SB measurements are made public on the official SKYSURF website and will be used to constrain Diffuse Light in future papers.

astro-ph.IM↗

arXiv2023

First semi-empirical test of the white dwarf mass-radius relationship using a single white dwarf via astrometric microlensing

In November 2019, the nearby single, isolated DQ-type white dwarf LAWD 37 (WD 1142-645) aligned closely with a distant background source and caused an astrometric microlensing event. Leveraging astrometry from \Gaia{} and followup data from the \textit{Hubble Space Telescope} we measure the astrometric deflection of the background source and obtain a gravitational mass for LAWD~37. The main challenge of this analysis is in extracting the lensing signal of the faint background source whilst it is buried in the wings of LAWD~37's point spread function. Removal of LAWD 37's point spread function induces a significant amount of correlated noise which we find can mimic the astrometric lensing signal. We find a deflection model including correlated noise caused by the removal of LAWD~37's point spread function best explains the data and yields a mass for LAWD 37 of $0.56\pm0.08 M_{\odot}$. This mass is in agreement with the theoretical mass-radius relationship and cooling tracks expected for CO core white dwarfs. Furthermore, the mass is consistent with no or trace amounts of hydrogen that is expected for objects with helium-rich atmospheres like LAWD 37. We conclude that further astrometric followup data on the source is likely to improve the inference on LAWD 37's mass at the $\approx3$ percent level and definitively rule out purely correlated noise explanations of the data. This work provides the first semi-empirical test of the white dwarf mass-radius relationship using a single, isolated white dwarf and supports current model atmospheres of DQ white dwarfs and white dwarf evolutionary theory.

astro-ph.SR↗