arXiv subjects

Jennifer Mack

Publications and source records attributed to Jennifer Mack.

15 recordsLinked to original sources

arXiv2026

Updates to WFC3/UVIS Encircled Energy Values in Select Filters

We present updated encircled energy (EE) curves for a subset of UVIS filters. These are derived from a reanalysis of the drizzled Point Spread Function (PSF) data underlying the current EE calibration together with new measurements from deep observations of the PSF wings. Improved centroiding and analysis techniques applied to the drizzled PSFs produce more accurate EE values at small radii ($r \le 10$ pixels), bringing the results into closer agreement with a large archival PSF study (Huynh et al. 2025). At large radii, we leverage deep observations of the PSF wings in six filters and compare the fraction of light between 2" and 6" with predictions from an optical model of the PSF (Hartig 2009). For filters with pivot wavelengths $ \gtrsim{4000} \mathrm{\mathring{A}}$, the model agrees with the empirical data, but over-estimates the EE for UV filters by $\sim0.5$% at 2". The revised EE solutions affect the UVIS zeropoints, which are derived from aperture photometry in a 0.4" (10 pixel) radius and corrected to 6" using EE tables (Calamida et al. 2022). Overall, the impact is small; the EE at 0.4" is larger by $ \gtrsim{0.5}$ % (0.005 mag) for several filters (F218W, F225W, F275W, F775W, F814W, F845M), especially for UVIS2. In contrast, the EE value is generally smaller at 0.4" for long-pass filters (F200LP, F350LP, F850LP), with F850LP differing by $\sim2 $ % (0.02 mag). Updated EE tables will be delivered together with a revised set of UVIS inverse sensitivity tables and zeropoints later in 2026. In the interim, we provide EE tables for commonly used filters in Appendix A.

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

Pixel-Based Non-Linearity Correction for the WFC3 IR Detector

The current non-linearity correction for the Wide Field Camera 3 Infrared (WFC3/IR) channel is based on ground-based data acquired during WFC3's Thermal Vacuum 3 (TV3) testing campaign. In the current reference file, the correction coefficients derived for each pixel are averaged over each of the four detector quadrants. In this work, we compute a new pixel-based non-linearity correction using in-flight calibration observations with the internal tungsten lamp flats acquired between 2011 and 2013. We derive the new correction coefficients by fitting a third-order polynomial to the accumulated signal ``up-the-ramp" for each pixel. Approximately 2\% of IR detector pixels are flagged as bad, and a solution cannot be computed. For these, we use the quadrant averages of the new correction coefficients. An accompanying report (\cite{huynh2025}) provides detailed testing results using both internal flats and external science targets acquired in a variety of observing modes. The report highlights improvements in photometry derived from ``\_flt.fits" data products calibrated using the new reference file, with the largest improvement for pixels with fluence levels approaching the full well limit of $\sim$80,000 $e^- $. A new NLINFILE reference file was delivered in October 2025 and will be used to reprocess all WFC3/IR imaging and grism observations in the MAST archive.

astro-ph.IM↗

arXiv2018

The Orbit of the Close Companion of Polaris: Hubble Space Telescope Imaging 2007 to 2014

As part of a program to determine dynamical masses of Cepheids, we have imaged the nearest and brightest Cepheid, Polaris, with the Hubble Space Telescope Wide Field Planetary Camera 2 and Wide Field Camera 3. Observations were obtained at three epochs between 2007 and 2014. In these images, as in HST frames obtained in 2005 and 2006, which we discussed in a 2008 paper, we resolve the close companion Polaris Ab from the Cepheid Polaris Aa. Because of the small separation and large magnitude difference between Polaris Aa and Ab, we used PSF deconvolution techniques to carry out astrometry of the binary. Based on these new measurements, we have updated the elements for the 29.59 yr orbit. Adopting the distance to the system from the recent Gaia Data Release 2, we find a dynamical mass for the Cepheid of 3.45 +/- 0.75 Msun, although this is preliminary, and will be improved by CHARA measurements covering periastron. As is the case for the recently determined dynamical mass for the Cepheid V1334 Cyg, the mass of Polaris is significantly lower than the "evolutionary mass" predicted by fitting to evolutionary tracks in the HR diagram. We discuss several questions and implications raised by these measurements, including the pulsation mode, which instability-strip crossing the stars are in, and possible complications such as rotation, mass loss, and binary mergers. The distant third star in the system, Polaris B, appears to be older than the Cepheid, based on isochrone fitting. This may indicate that the Cepheid Polaris is relatively old and is the result of a binary merger, rather than being a young single star.

astro-ph.SR↗

arXiv2018

Multi-View Semantic Labeling of 3D Point Clouds for Automated Plant Phenotyping

Semantic labeling of 3D point clouds is important for the derivation of 3D models from real world scenarios in several economic fields such as building industry, facility management, town planning or heritage conservation. In contrast to these most common applications, we describe in this study the semantic labeling of 3D point clouds derived from plant organs by high-precision scanning. Our approach is optimized for the task of plant phenotyping with its very specific challenges and is employing a deep learning framework. Thereby, we report important experiences concerning detailed parameter initialization and optimization techniques. By evaluating our approach with challenging datasets we achieve state-of-the-art results without difficult and time consuming feature engineering as being necessary in traditional approaches to semantic labeling.

cs.CV↗

arXiv2014

DrizzlePac 2.0 - Introducing New Features

The DrizzlePac package includes tasks for aligning and drizzling images taken with the Hubble Space Telescope. We present this release which includes new features that facilitate image alignment, sky matching, and adds support for new time dependent distortion solutions of the ACS instrument. The TweakReg task now includes capabilities for automatically aligning images which form part of a mosaic. In addition, new parameters make it easier to reject cosmic rays and other spurious detections from source catalogs used for alignment. The Astrodrizzle task has been improved with a new sky matching algorithm which makes producing mosaics easier than ever before. This new version supports an improved version of the ACS/WFC time-dependent distortion correction. There are also improvements to the GUI interfaces and some behind the scene bug fixes.

astro-ph.IM↗

arXiv2008

A New Hubble Space Telescope Distance to NGC 1569: Starburst Properties and IC 342 Group Membership

We present deep HST ACS/WFC photometry of the dwarf irregular galaxy NGC 1569, one of the closest and strongest nearby starburst galaxies. These data allow us, for the first time, to unequivocally detect the tip of the red giant branch and thereby determine the distance to NGC 1569. We find that this galaxy is 3.36 +/- 0.20 Mpc away, considerably farther away than the typically assumed distance of 2.2 +/- 0.6 Mpc. Previously thought to be an isolated galaxy due to its shorter distance, our new distance firmly establishes NGC 1569 as a member of the IC 342 group of galaxies. The higher density environment may help explain the starburst nature of NGC 1569, since starbursts are often triggered by galaxy interactions. On the other hand, the longer distance implies that NGC 1569 is an even more extreme starburst galaxy than previously believed. Previous estimates of the rate of star formation for stars younger than ~ 1 Gyr become stronger by more than a factor of 2. Stars older than this were not constrained by previous studies. The dynamical masses of NGC 1569's three super star clusters, which are already known as some of the most massive ever discovered, increase by ~53% to 6-7x10^5 solar masses.

astro-ph↗

arXiv2002

The Hubble Deep Field South Flanking Fields

As part of the Hubble Deep Field South program, a set of shorter 2-orbit observations were obtained of the area adjacent to the deep fields. The WFPC2 flanking fields cover a contiguous solid angle of 48 square arcminutes. Parallel observations with the STIS and NICMOS instruments produce a patchwork of additional fields with optical and near-infrared (1.6 micron) response. Deeper parallel exposures with WFPC2 and NICMOS were obtained when STIS observed the NICMOS deep field. These deeper fields are offset from the rest, and an extended low surface brightness object is visible in the deeper WFPC2 flanking field. In this data paper, which serves as an archival record of the project, we discuss the observations and data reduction, and present SExtractor source catalogs and number counts derived from the data. Number counts are broadly consistent with previous surveys from both ground and space. Among other things, these flanking field observations are useful for defining slit masks for spectroscopic follow-up over a wider area around the deep fields, for studying large-scale structure that extends beyond the deep fields, for future supernova searches, and for number counts and morphological studies, but their ultimate utility will be defined by the astronomical community.

astro-ph↗

arXiv2001

Distant Cluster Hunting I: A Comparison Between the Optical and X-ray Luminosity Functions from an Optical/X-ray Survey

We present a comparison of X-ray and optical luminosities and luminosity functions of cluster candidates from a joint optical/X-ray survey, the ROSAT Optical X-Ray Survey. Completely independent X-ray and optical catalogs of 23 ROSAT fields (4.8 deg2) were created by a matched-filter optical algorithm and by a wavelet technique in the X-ray. We directly compare the results of the optical and X-ray selection techniques. The matched-filter technique detected 74% (26 out of 35) of the most reliable cluster candidates in the X-ray-selected sample; the remainder could be either constellations of X-ray point sources or z>1 clusters. The matched-filter technique identified approximately 3 times the number of candidates (152 candidates) found in the X-ray survey of nearly the same sky (57 candidates). While the estimated optical and X-ray luminosities of clusters of galaxies are correlated, the intrinsic scatter in this relationship is very large. We can reproduce the number and distribution of optical clusters with a model defined by the X-ray luminosity function and by an LX Lambda cl relation if H0=75 km s-1 Mpc-1 and if the LX Lambda cl relation is steeper than the expected LX Lambda 2cl. On statistical grounds, a bimodal distribution of X-ray luminous and X-ray faint clusters is unnecessary to explain our observations. Follow-up work is required to confirm whether the clusters without bright X-ray counterparts are simply X-ray faint for their optical luminosity because of their low mass or youth or are a distinct population of clusters that do not, for some reason, have dense intracluster media. We suspect that these optical clusters are low-mass systems, with correspondingly low X-ray temperatures and luminosities, or that they are not yet completely virialized systems.

astro-ph↗

arXiv2001

Distant Cluster Hunting II: A comparison of X-ray and optical cluster detection techniques and catalogs from the ROX Survey

We present and analyze the optical and X-ray catalogs of moderate-redshift cluster candidates from the ROSAT Optical X-ray Survey, or ROXS. The survey covers 4.8 square degrees (23 ROSAT PSPC pointings). The cross-correlated cluster catalogs were constructed by comparing two independent catalogs extracted from the optical and X-ray bandpasses, using a matched filter technique for the optical data and a wavelet technique for the X-ray data. We cross-id cluster candidates in each catalog. In Paper II we present the cluster catalogs and a numerical simulation of ROXS. We also present color-magnitude plots for several cluster candidates, and examine the prominence of the red sequence in each. We find that the X-ray clusters analyzed in this way do not all have a prominent red sequence. We conclude that while the red sequence may be distinct for massive, virialized clusters, it may be less so for lower-mass clusters at even moderate redshifts. Multiple, complementary methods of selecting and defining clusters may be essential, particularly at high redshift where all methods run into completeness limits, incomplete understanding of physical evolution, and projection effects.

astro-ph↗

arXiv2001

Dynamical Friction in dE Globular Cluster Systems

The dynamical friction timescale for globular clusters to sink to the center of a dwarf elliptical galaxy (dE) is significantly less than a Hubble time if the halos have King-model or isothermal profiles and the globular clusters formed with the same radial density profile as the underlying stellar population. We examine the summed radial distribution of the entire globular cluster systems and the bright globular cluster candidates in 51 Virgo and Fornax Cluster dEs for evidence of dynamical friction processes. We find that the summed distribution of the entire globular cluster population closely follows the exponential profile of the underlying stellar population. However, there is a deficit of bright clusters within the central regions of dEs (excluding the nuclei), perhaps due to the orbital decay of these massive clusters into the dE cores. We also predict the magnitude of each dE's nucleus assuming the nuclei form via dynamical friction. The observed trend of decreasing nuclear luminosity with decreasing dE luminosity is much stronger than predicted if the nuclei formed via simple dynamical friction processes. We find that the bright dE nuclei could have been formed from the merger of orbitally decayed massive clusters, but the faint nuclei are several magnitudes fainter than expected. These faint nuclei are found primarily in M_V > -14 dEs which have high globular cluster specific frequencies and extended globular cluster systems. In these galaxies, supernovae-driven winds, high central dark matter densities, extended dark matter halos, the formation of new star clusters, or tidal interactions may act to prevent dynamical friction from collapsing the entire globular cluster population into a single bright nucleus.

astro-ph↗

arXiv2000

Kinematics, ages, and metallicities of star clusters in NGC 1316: A 3 Gyr old merger remnant

We report on multi-object spectroscopy of 37 candidate star clusters around the giant early-type radio galaxy NGC 1316 (Fornax A), the brightest galaxy in the Fornax cluster. For the star clusters in this sample, we measure a mean radial velocity of 1698 +/- 46 km/s, a rotation velocity of 175 +/- 70 km/s, and a velocity dispersion of 227 +/- 33 km/s within a galactocentric radius of 24 kpc. Using the projected mass estimator and assuming isotropic orbits, the estimated total mass is (6.6 +/- 1.7) E+11 solar masses within a radius of 24 kpc. The mass is uncertain by about a factor of two, depending on the orbital assumptions. The implied M/L_B ratio is in the range 3-6. Four star clusters in our sample are exceptionally luminous (M_V < -12.3). This means that (1) at least this many clusters in NGC 1316 are up to an order of magnitude more luminous than the most luminous star cluster in our Galaxy or M31, and (2) that the S/N ratio of their spectra allows us to measure line strengths with good accuracy. By comparing the colours and equivalent widths of H-alpha and the Ca II triplet absorption lines for those bright star clusters in our sample with those of single-burst population models, we find that they are coeval with an age of 3.0 +/- 0.5 Gyr. Their metallicities are found to be solar to within 0.15 dex. These results show once again that globular clusters with near-solar metallicity do form during galactic mergers, and, moreover, that they can survive disruption processes taking place during the merger (e.g., dynamical friction, tidal disruption), as well as evaporation. In this respect, NGC 1316 provides a hitherto "missing" evolutionary link between young merger remnants of age ~0.5 Gyr such as NGC 3597, NGC 3921 and NGC 7252 on one side, and older giant ellipticals featuring bimodal colour distributions on the other side.

astro-ph↗

arXiv2000

WFPC2 Observations of the Hubble Deep Field-South

The Hubble Deep Field-South observations targeted a high-galactic-latitude field near QSO J2233-606. We present WFPC2 observations of the field in four wide bandpasses centered at roughly 300, 450, 606, and 814 nm. Observations, data reduction procedures, and noise properties of the final images are discussed in detail. A catalog of sources is presented, and the number counts and color distributions of the galaxies are compared to a new catalog of the HDF-N that has been constructed in an identical manner. The two fields are qualitatively similar, with the galaxy number counts for the two fields agreeing to within 20%. The HDF-S has more candidate Lyman-break galaxies at z > 2 than the HDF-N. The star-formation rate per unit volume computed from the HDF-S, based on the UV luminosity of high-redshift candidates, is a factor of 1.9 higher than from the HDF-N at z ~ 2.7, and a factor of 1.3 higher at z ~ 4.

astro-ph↗

arXiv2000

HST Observations of Vibrationally-Excited Molecular Hydrogen in Cluster Cooling Flow Nebulae

We report new HST NICMOS and WFPC2 imaging of emission-line nebulae in the central galaxies of 3 clusters of galaxies purported to host massive cooling flows, NGC1275, A2597, and PKS0745. The spectral signature of vibrationally- excited molecular hydrogen (VEMH) has been seen in every galaxy searched so far in a cluster cooling flow with an optical emission line nebula. We have discovered that the VEMH gas extends several kpc from the centers of A2597 and PKS0745, while the vibrationally-excited molecular hydrogen in NGC1275 appears to be mostly confined to its nucleus, with some extended emission <1 kpc from the center. The VEMH in A2597 and PKS0745-191 seems to be nearly co-spatial with the optical emission-line filaments in those systems. Candidates for heating the nebulae are X-ray irradiation by the ICM, UV fluorescence by young stars, and shocks. UV heating by young stars provides the most satisfactory explanation for the H2 emission in A2597 and PKS0745; X-ray irradiation is energetically unlikely and strong shocks (v>40 km/s) are ruled out by the high H2/H-alpha ratios. If UV heating is the main energy input, a few billion solar masses of molecular gas is present in A2597 and PKS0745. UV irradiation models predict a significant amount of 1-2 micron emission from higher excitation H2 transitions and moderate far infrared luminosities (~1e44/h^2 erg/s) for A2597 and PKS0745. Even in the context of UV fluorescence models, the total amount of H2 gas and star formation inferred from these observations is too small to account for the cooling flow rates and longevities inferred from the X-rays. We note an interesting new constraint on cooling flow models: the radio sources do not provide a significant amount of shock heating, and therefore cannot counterbalance the cooling of the X-ray gas in the cluster cores.

astro-ph↗