Anthony J. Remijan

The Catholic University of America, Washington, Washington, D.C., United States

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Publications (109)303.47 Total impact

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    ABSTRACT: We present Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region. The continuum images at wavelengths of 2.9, 1.3, and 0.87 mm have unprecedented angular resolutions of 0.075 arcseconds (10 AU) to 0.025 arcseconds (3.5 AU), revealing an astonishing level of detail in the circumstellar disk surrounding the young solar analogue HL Tau, with a pattern of bright and dark rings observed at all wavelengths. By fitting ellipses to the most distinct rings, we measure precise values for the disk inclination (46.72pm0.05 degrees) and position angle (+138.02pm0.07 degrees). We obtain a high-fidelity image of the 1.0 mm spectral index ($\alpha$), which ranges from $\alpha\sim2.0$ in the optically-thick central peak and two brightest rings, increasing to 2.3-3.0 in the dark rings. The dark rings are not devoid of emission, we estimate a grain emissivity index of 0.8 for the innermost dark ring and lower for subsequent dark rings, consistent with some degree of grain growth and evolution. Additional clues that the rings arise from planet formation include an increase in their central offsets with radius and the presence of numerous orbital resonances. At a resolution of 35 AU, we resolve the molecular component of the disk in HCO+ (1-0) which exhibits a pattern over LSR velocities from 2-12 km/s consistent with Keplerian motion around a ~1.3 solar mass star, although complicated by absorption at low blue-shifted velocities. We also serendipitously detect and resolve the nearby protostars XZ Tau (A/B) and LkHa358 at 2.9 mm.
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    ABSTRACT: We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum images of the asteroid 3 Juno obtained with an angular resolution of 0.042 arcseconds (60 km at 1.97 AU). The data were obtained over a single 4.4 hr interval, which covers 60% of the 7.2 hr rotation period, approximately centered on local transit. A sequence of ten consecutive images reveals continuous changes in the asteroid's profile and apparent shape, in good agreement with the sky projection of the three-dimensional model of the Database of Asteroid Models from Inversion Techniques. We measure a geometric mean diameter of 259pm4 km, in good agreement with past estimates from a variety of techniques and wavelengths. Due to the viewing angle and inclination of the rotational pole, the southern hemisphere dominates all of the images. The median peak brightness temperature is 215pm13 K, while the median over the whole surface is 197pm15 K. With the unprecedented resolution of ALMA, we find that the brightness temperature varies across the surface with higher values correlated to the subsolar point and afternoon areas, and lower values beyond the evening terminator. The dominance of the subsolar point is accentuated in the final four images, suggesting a reduction in the thermal inertia of the regolith at the corresponding longitudes, which are possibly correlated to the location of the putative large impact crater. These results demonstrate ALMA's potential to resolve thermal emission from the surface of main belt asteroids, and to measure accurately their position, geometric shape, rotational period, and soil characteristics.
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    ABSTRACT: We present initial results of very high resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations of the $z$=3.042 gravitationally lensed galaxy HATLAS J090311.6+003906 (SDP.81). These observations were carried out using an extended configuration as part of Science Verification for the 2014 ALMA Long Baseline Campaign, with baselines of up to 15 km. We present continuum imaging at 151, 236 and 290 GHz, at angular resolutions as fine as 23 milliarcseconds (mas; corresponding to an un-magnified spatial scale of 180 pc at z=3.042). The ALMA images clearly show two main gravitational arc components with emission tracing a radius of 1.5". We also present imaging of CO(10-9), CO(8-7), CO(5-4) and H2O line emission. The CO data has an angular resolution of 170 mas and the emission is found to broadly trace the gravitational arc structures. We detect H2O line emission but only using the shortest baselines. The ALMA continuum and spectral line fluxes are consistent with previous Plateau de Bure Interferometer and Submillimeter Array observations despite the increase in angular resolution. Finally, we detect weak unresolved continuum emission at all three observed frequencies from a position that is spatially coincident with the centre of the foreground lensing galaxy.
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    ABSTRACT: The bandwith, sensitivity and sheer survey speed of the SKA offers unique potential for deep spectroscopic surveys of the Milky Way. Within the frequency bands available to the SKA lie many transitions that trace the ionised, radical and molecular components of the interstellar medium and which will revolutionise our understanding of many physical processes. In this chapter we describe the impact on our understanding of the Milky Way that can be achieved by spectroscopic SKA surveys, including "out of the box" early science with radio recombination lines, Phase 1 surveys of the molecular ISM using anomalous formaldehyde absorption, and full SKA surveys of ammonia inversion lines.
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    ABSTRACT: An extensive search has been conducted to confirm transitions of \textit{trans}-ethyl methyl ether (tEME, C$_2$H$_5$OCH$_3$), toward the high mass star forming region W51 e1/e2 using the 12 m Telescope of the Arizona Radio Observatory (ARO) at wavelengths from 2 mm and 3 mm. In short, we cannot confirm the detection of tEME toward W51 e1/e2 and our results call into question the initial identification of this species by \citet{FuchsSpace}. Additionally, reevaluation of the data from the original detection indicates that tEME is not present toward W51 e1/e2 in the abundance reported by Fuchs and colleagues. Typical peak-to-peak noise levels for the present observations of W51 e1/e2 were between 10 - 30 mK, yielding an upper limit of the tEME column density of $\leq$ 1.5 $\times$ 10$^{15}$ cm$^{-2}$. This would make tEME at least a factor 2 times less abundant than dimethyl ether (CH$_3$OCH$_3$) toward W51 e1/e2. We also performed an extensive search for this species toward the high mass star forming region Sgr B2(N-LMH) with the NRAO 100 m Green Bank Telescope (GBT). No transitions of tEME were detected and we were able to set an upper limit to the tEME column density of $\leq$ 4 $\times$ 10$^{14}$ cm$^{-2}$ toward this source. Thus, we are able to show that tEME is not a new molecular component of the interstellar medium and that an exacting assessment must be carried out when assigning transitions of new molecular species to astronomical spectra to support the identification of large organic interstellar molecules.
    The Astrophysical Journal 11/2014; 799(1). DOI:10.1088/0004-637X/799/1/15 · 6.28 Impact Factor
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    ABSTRACT: Recently, Lattelais et al. (2009) have interpreted aggregated observations of molecular isomers to suggest that there exists a "minimum energy principle'', such that molecular formation will favor more stable molecular isomers for thermodynamic reasons. To test the predictive power of this principle, we have fully characterized the spectra of the three isomers of C$_{3}$H$_{2}$O toward the well known molecular region Sgr B2(N). Evidence for the detection of the isomers cyclopropenone (c-C$_{3}$H$_{2}$O) and propynal (HCCCHO) is presented, along with evidence for the non-detection of the lowest zero-point energy isomer, propadienone (CH$_2$CCO). We interpret these observations as evidence that chemical formation pathways, which may be under kinetic control, have a more pronounced effect on final isomer abundances than thermodynamic effects such as the minimum energy principle.
    The Astrophysical Journal 10/2014; 799(1). DOI:10.1088/0004-637X/799/1/34 · 6.28 Impact Factor
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    ABSTRACT: We present spectrally and spatially resolved maps of HNC and HC3N emission from Titan's atmosphere, obtained using the Atacama Large Millimeter/submillimeter Array on 2013 November 17. These maps show anisotropic spatial distributions for both molecules, with resolved emission peaks in Titan's northern and southern hemispheres. The HC3N maps indicate enhanced concentrations of this molecule over the poles, consistent with previous studies of Titan's photochemistry and atmospheric circulation. Differences between the spectrally integrated flux distributions of HNC and HC3N show that these species are not co-spatial. The observed spectral line shapes are consistent with HNC being concentrated predominantly in the mesosphere and above (at altitudes z 400 km), whereas HC3N is abundant at a broader range of altitudes (z 70-600 km). From spatial variations in the HC3N line profile, the locations of the HC3N emission peaks are shown to be variable as a function of altitude. The peaks in the integrated emission from HNC and the line core (upper atmosphere) component of HC3N (at z 300 km) are found to be asymmetric with respect to Titan's polar axis, indicating that the mesosphere may be more longitudinally variable than previously thought. The spatially integrated HNC and HC3N spectra are modeled using the NEMESIS planetary atmosphere code and the resulting best-fitting disk-averaged vertical mixing ratio profiles are found to be in reasonable agreement with previous measurements for these species. Vertical column densities of the best-fitting gradient models for HNC and HC3N are 1.9 × 1013 cm–2 and 2.3 × 1014 cm–2, respectively.
    The Astrophysical Journal Letters 10/2014; 795(2):L30. DOI:10.1088/2041-8205/795/2/L30 · 5.60 Impact Factor
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    ABSTRACT: We present the highest spatial resolution (~0.5") CO (3-2) observations to date of the "overlap" region in the merging Antennae galaxies (NGC 4038/39), taken with the ALMA. We report on the discovery of a long (3 kpc), thin (aspect ratio 30/1), filament of CO gas which breaks up into roughly ten individual knots. Each individual knot has a low internal velocity dispersion (~10 km/s), and the dispersion of the ensemble of knots in the filament is also low (~10 km/s). At the other extreme, we find that the individual clouds in the Super Giant Molecular Cloud 2 region discussed by Wilson and collaborators have a large range of internal velocity dispersions (10 to 80 km/s), and a large dispersion amongst the ensemble (~80 km/s). We use a combination of optical and near-IR data from HST, radio continuum observations taken with the VLA, and CO data from ALMA to develop an evolutionary classification system which provides a framework for studying the sequence of star cluster formation and evolution, from diffuse SGMCs, to proto, embedded, emerging, young, and intermediate/old clusters. The relative timescales have been assessed by determining the fractional population of sources at each evolutionary stage. Using the evolutionary framework, we estimate the maximum age range of clusters in a single SGMC is ~10 Myr, which suggests that the molecular gas is removed over this timescale resulting in the cessation of star formation and the destruction of the GMC within a radius of about 200 pc. (abridged)
    The Astrophysical Journal 10/2014; 795(2). DOI:10.1088/0004-637X/795/2/156 · 6.28 Impact Factor
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    ABSTRACT: Sgr B2 is an active high mass star forming region in the Galactic center and the pre-eminent interstellar source of organic chemistry. Newly available broad bandwidth radio interferometry data enables a spatially resolved study of the chemical environments within the Sgr B2(N) core. We present selections from a 30 - 50 GHz spectral line survey conducted with the ATCA.
    Proceedings of the International Astronomical Union 10/2014; 9(S303):205-207. DOI:10.1017/S174392131400057X
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    ABSTRACT: We present spectrally and spatially-resolved maps of HNC and HC$_3$N emission from Titan's atmosphere, obtained with the Atacama Large Millimeter Array (ALMA) on 2013 November 17. These maps show anisotropic spatial distributions for both molecules, with resolved emission peaks in Titan's northern and southern hemispheres. The HC$_3$N maps indicate enhanced concentrations of this molecule over the poles, consistent with previous studies of Titan's photochemistry and atmospheric circulation. Differences between the integrated flux distributions of HNC and HC$_3$N show that these species are not co-spatial. The observed spectral line shapes are consistent with HNC residing predominantly in the mesosphere and above (at altitudes $z$ greater than about 400 km), whereas HC$_3$N is abundant at a broader range of altitudes ($z\approx70-500$ km). From spatial variations in the HC$_3$N line profile, the locations of the HC$_3$N emission peaks are shown to be variable as a function of altitude. The integrated emission peaks for HNC and the upper-atmosphere HC$_3$N component (at $z\gtrsim300$ km) are found to be asymmetric with respect to Titan's polar axis, indicating that the mesosphere may be more longitudinally-variable than previously thought. Disk-averaged HNC and HC$_3$N spectra are modeled using the RADTRANS planetary atmosphere code and the resulting best-fitting vertical mixing ratio (VMR) profiles are found to be in reasonable agreement with previous measurements for these species.
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    ABSTRACT: Results are presented from the first cometary observations using the Atacama Large Millimeter/Submillimeter Array (ALMA), including measurements of the spatially-resolved distributions of HCN, HNC, H$_2$CO and dust within the comae of two comets: C/2012 F6 (Lemmon) and C/2012 S1 (ISON), observed at heliocentric distances of 1.5 AU and 0.54 AU, respectively. These observations (with angular resolution $\approx0.5''$), reveal an unprecedented level of detail in the distributions of these fundamental cometary molecules, and demonstrate the power of ALMA for quantitative measurements of the distributions of molecules and dust in the inner comae of typical bright comets. In both comets, HCN is found to originate from (or within a few hundred km of) the nucleus, with a spatial distribution largely consistent with spherically-symmetric, uniform outflow. By contrast, the HNC distributions are clumpy and asymmetrical, with peaks at cometocentric radii $\sim$500-1000~km, consistent with release of HNC in collimated outflow(s). Compared to HCN, the H$_2$CO distribution in comet Lemmon is very extended. The interferometric visibility amplitudes are consistent with coma production of H$_2$CO and HNC from unidentified precursor material(s) in both comets. Adopting a Haser model, the H$_2$CO parent scale-length is found to be a few thousand km in Lemmon and only a few hundred km in ISON, consistent with destruction of the precursor by photolysis or thermal degradation at a rate which scales in proportion to the Solar radiation flux.
    The Astrophysical Journal 08/2014; 792(1):L2. DOI:10.1088/2041-8205/792/1/L2 · 6.28 Impact Factor
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    ABSTRACT: The transition from construction to full operations of the Atacama Large Millimeter/submillimeter Array (ALMA) brings the challenge to have not only software subsystems that are functional and stable but also to develop a system that works flawlessly as a single entity from proposal preparation to the delivery of the final data products to ALMA users. This is especially challenging as the different subsystems have to be constantly updated and improved to accommodate new observing modes and increasing capabilities. We present recent progress and future initiatives in the different offline subsystems that are currently being developed and used in ALMA operations: proposal preparation, submission and observation preparation (Observing Tool and submission server), proposal review process (Ph1M), project tracking (Project Tracker, Life Cycle), observation bookkeeping (Shift Log Tool), calibrator database (Source Catalogue), monitor and control of observations (Operations Monitoring and Control tool), dynamic scheduler, data reduction pipeline, quality assurance and trend analysis (AQUA), archive, as well as additional user support systems such as the Science Portal.
    SPIE Astronomical Telescopes + Instrumentation; 08/2014
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    ABSTRACT: The Jupiter-family comet 103P/Hartley 2 (103P) was the target of the NASA EPOXI mission. In support of this mission, we conducted observations from radio to submillimeter wavelengths of comet 103P in the three weeks preceding the spacecraft rendezvous on UT 2010 November 4.58. This time period included the passage at perihelion and the closest approach of the comet to the Earth. Here we report detections of HCN, H2CO, CS, and OH and upper limits for HNC and DCN towards 103P, using the Arizona Radio Observatory Kitt Peak 12m telescope (ARO 12m) and submillimeter telescope (SMT), the James Clerk Maxwell Telescope (JCMT) and the Greenbank Telescope (GBT). The water production rate, QH2O = (0.67 - 1.07) x 10^28 s^-1, was determined from the GBT OH data. From the average abundance ratios of HCN and H2CO relative to water (0.13 +/- 0.03 % and 0.14 +/- 0.03 %, respectively), we conclude that H2CO is depleted and HCN is normal with respect to typically-observed cometary mixing ratios. However, the abundance ratio of HCN with water shows a large diversity with time. Using the JCMT data we measured an upper limit for the DCN/HCN ratio <0.01. Consecutive observations of ortho- H2CO and para-H2CO on November 2 (from data obtained at the JCMT), allowed us to derive an ortho : para ratio (OPR) ~ 2.12 +/- 0.59 (1sigma), corresponding to Tspin > 8 K (2sigma).
    The Astrophysical Journal 07/2014; 794(1). DOI:10.1088/0004-637X/794/1/1 · 6.28 Impact Factor
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    ABSTRACT: The results of a Caltech Submillimeter Observatory (CSO) search for $l$-C$_3$H$^+$, first detected by Pety et al. (2012) in observations toward the Horsehead photodissociation region (PDR), are presented. A total of 39 sources were observed in the 1 mm window. Evidence of emission from $l$-C$_3$H$^+$ is found in only a single source - the Orion Bar PDR region, which shows a rotational temperature of 178(13) K and a column density of 7(2) x $10^{11}$ cm$^{-2}$. In the remaining sources, upper limits of ~10$^{11} - 10^{13}$ cm$^{-2}$ are found. These results are discussed in the context of guiding future observational searches for this species.
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    ABSTRACT: Pety et al. have reported the detection of eight transitions of a closed-shell, linear molecule (B11244) in observations toward the Horsehead photodissociation region (PDR), which they attribute to the l-C3H+ cation. Recent high-level ab initio calculations have called this assignment into question; the anionic C3H─ molecule has been suggested as a more likely candidate. Here, we examine observations of the Horsehead PDR, Sgr B2(N), TMC-1, and IRC+10216 in the context of both l-C3H+ and C3H─. We find no observational evidence of Ka = 1 lines, which should be present were the carrier indeed C3H─. Additionally, we find a strong anticorrelation between the presence of known molecular anions and B11244 in these regions. Finally, we discuss the formation and destruction chemistry of C3H─ in the context of the physical conditions in the regions. Based on these results, we conclude there is little evidence to support the claim that the carrier is C3H─.
    The Astrophysical Journal 03/2014; 783(1):36. DOI:10.1088/0004-637X/783/1/36 · 6.28 Impact Factor
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    ABSTRACT: We will present molecular and continuum submillimeter observerations of Comet C/2012 S1 (ISON) pre-perihelion, during outbursts, and the final break-up event.

Publication Stats

1k Citations
303.47 Total Impact Points

Institutions

  • 2014
    • The Catholic University of America
      • Department of Physics
      Washington, Washington, D.C., United States
  • 2006–2014
    • National Radio Astronomy Observatory
      Charlottesville, Virginia, United States
  • 2005–2010
    • University of Illinois, Urbana-Champaign
      • Department of Astronomy
      Urbana, Illinois, United States