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Milne P.A.,University of Arizona | Williams G.G.,University of Arizona | Williams G.G.,MMT Observatory | Porter A.,Clemson University | And 5 more authors.
Astrophysical Journal | Year: 2017

We present multiple spectropolarimetric observations of the nearby Type Ia supernova (SN) 2011fe in M101, obtained before, during, and after the time of maximum apparent visual brightness. The excellent time coverage of our spectropolarimetry has allowed better monitoring of the evolution of polarization features than is typical, which has allowed us new insight into the nature of normal SNe Ia. SN 2011fe exhibits time-dependent polarization in both the continuum and strong absorption lines. At early epochs, red wavelengths exhibit a degree of continuum polarization of up to 0.4%, likely indicative of a mild asymmetry in the electron-scattering photosphere. This behavior is more common in subluminous SNe Ia than in normal events, such as SN 2011fe. The degree of polarization across a collection of absorption lines varies dramatically from epoch to epoch. During the earliest epoch, a λ4600-5000 Å complex of absorption lines shows enhanced polarization at a different position angle than the continuum. We explore the origin of these features, presenting a few possible interpretations, without arriving at a single favored ion. During two epochs near maximum, the dominant polarization feature is associated with the Si ii λ6355 Å absorption line. This is common for SNe Ia, but for SN 2011fe the polarization of this feature increases after maximum light, whereas for other SNe Ia, that polarization feature was strongest before maximum light. © 2017. The American Astronomical Society. All rights reserved.


Cool R.J.,MMT Observatory | Moustakas J.,Siena College | Blanton M.R.,New York University | Burles S.M.,D.E. Shaw and Co. L.P | And 9 more authors.
Astrophysical Journal | Year: 2013

The PRIsm MUlti-object Survey (PRIMUS) is a spectroscopic galaxy redshift survey to z ∼ 1 completed with a low-dispersion prism and slitmasks allowing for simultaneous observations of ∼2500 objects over 0.18 deg2. The final PRIMUS catalog includes ∼130,000 robust redshifts over 9.1 deg2. In this paper, we summarize the PRIMUS observational strategy and present the data reduction details used to measure redshifts, redshift precision, and survey completeness. The survey motivation, observational techniques, fields, target selection, slitmask design, and observations are presented in Coil et al. Comparisons to existing higher-resolution spectroscopic measurements show a typical precision of σ z /(1 + z) = 0.005. PRIMUS, both in area and number of redshifts, is the largest faint galaxy redshift survey completed to date and is allowing for precise measurements of the relationship between active galactic nuclei and their hosts, the effects of environment on galaxy evolution, and the build up of galactic systems over the latter half of cosmic history. © 2013. The American Astronomical Society. All rights reserved..


Mauerhan J.,University of California at Berkeley | Mauerhan J.,University of Arizona | Williams G.G.,University of Arizona | Williams G.G.,MMT Observatory | And 9 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present spectropolarimetry of SN 2009ip throughout the evolution of its 2012 explosion. During the 2012a phase, when the spectrum exhibits broad P-Cygni lines, we measure a V-band polarization of P ≈ 0.9 per cent at a position angle of θ ≈ 166o, indicating substantial asphericity for the 2012a outflow. Near the subsequent peak of the 2012b phase, when the spectrum shows signs of intense interaction with circumstellar material (CSM), we measure P ≈ 1.7 per cent and θ ≈ 72o, indicating a separate component of polarization during 2012b, which exhibits a higher degree of asphericity than 2012a and an orthogonal axis of symmetry on the sky. Around 30 d past peak, coincident with a substantial bump in the declining light curve, we measure P≈0.7 per cent and another significant shift in θ.At this point, broad photospheric lines have again become prominent and exhibit significant variations in P relative to the continuum, particularly He I/Na ID. By 60 d past peak, the continuum polarization has dropped below 0.2 per cent, probably declining towards a low value of interstellar polarization. The results are consistent with a scenario in which a prolate (possibly bipolar) explosion launched during the 2012a phase impacts an oblate (toroidal) distribution of CSM in 2012b. Previous calculations that assumed spherical symmetry for the CSM have substantially underestimated the required explosion energy, since only a small fraction of the SN ejecta appears to have participated in strong CSM interaction. A kinetic energy of ~1051 erg is difficult to avoid, supporting the interpretation that the 2012 outburst of SN 2009ip was the result of a corecollapse explosion. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Comerford J.M.,University of Colorado at Boulder | Comerford J.M.,University of Texas at Austin | Schluns K.,Boston University | Greene J.E.,Princeton University | Cool R.J.,MMT Observatory
Astrophysical Journal | Year: 2013

Dual supermassive black holes (SMBHs) with kiloparsec-scale separations in merger-remnant galaxies are informative tracers of galaxy evolution, but the avenue for identifying them in large numbers for such studies is not yet clear. One promising approach is to target spectroscopic signatures of systems where both SMBHs are fueled as dual active galactic nuclei (AGNs), or where one SMBH is fueled as an offset AGN. Dual AGNs may produce double-peaked narrow AGN emission lines, while offset AGNs may produce single-peaked narrow AGN emission lines with line-of-sight velocity offsets relative to the host galaxy. We search for such dual and offset systems among 173 Type 2 AGNs at z < 0.37 in the AGN and Galaxy Evolution Survey (AGES), and we find two double-peaked AGNs and five offset AGN candidates. When we compare these results to a similar search of the DEEP2 Galaxy Redshift Survey and match the two samples in color, absolute magnitude, and minimum velocity offset, we find that the fraction of AGNs that are dual SMBH candidates increases from z = 0.25 to z = 0.7 by a factor of ∼6 (from 2/70 to 16/91, or to ). This may be associated with the rise in the galaxy merger fraction over the same cosmic time. As further evidence for a link with galaxy mergers, the AGES offset and dual AGN candidates are tentatively ∼3 times more likely than the overall AGN population to reside in a host galaxy that has a companion galaxy (from 16/173 to 2/7, or to ). Follow-up observations of the seven offset and dual AGN candidates in AGES will definitively distinguish velocity offsets produced by dual SMBHs from those produced by narrow-line region kinematics, and will help sharpen our observational approach to detecting dual SMBHs. © 2013. The American Astronomical Society. All rights reserved.


Jensen E.A.,ACS Consulting | Jensen E.A.,MMT Observatory | Hick P.P.,University of California at San Diego | Bisi M.M.,Institute of Mathematical and Physical science | And 4 more authors.
Solar Physics | Year: 2010

We present the results from modeling the coronal mass ejection (CME) properties that have an effect on the Faraday rotation (FR) signatures that may be measured with an imaging radio antenna array such as the Murchison Widefield Array (MWA). These include the magnetic flux rope orientation, handedness, magnetic-field magnitude, velocity, radius, expansion rate, electron density, and the presence of a shock/sheath region. We find that simultaneous multiple radio source observations (FR imaging) can be used to uniquely determine the orientation of the magnetic field in a CME, increase the advance warning time on the geoeffectiveness of a CME by an order of magnitude from the warning time possible from in-situ observations at L1, and investigate the extent and structure of the shock/sheath region at the leading edge of fast CMEs. The magnetic field of the heliosphere is largely "invisible" with only a fraction of the interplanetary magnetic-field lines convecting past the Earth; remote sensing the heliospheric magnetic field through FR imaging from the MWA will advance solar physics investigations into CME evolution and dynamics. © 2010 The Author(s).


Powell K.B.,MMT Observatory | Vaitheeswaran V.,Steward Observatory
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

The MMT observatory has recently implemented and tested an optimal wavefront controller for the NGS adaptive optics system. Open loop atmospheric data collected at the telescope is used as the input to a MATLAB based analytical model. The model uses nonlinear constrained minimization to determine controller gains and optimize the system performance. The real-time controller performing the adaptive optics close loop operation is implemented on a dedicated high performance PC based quad core server. The controller algorithm is written in C and uses the GNU scientific library for linear algebra. Tests at the MMT confirmed the optimal controller significantly reduced the residual RMS wavefront compared with the previous controller. Significant reductions in image FWHM and increased peak intensities were obtained in J, H and K-bands. The optimal PID controller is now operating as the baseline wavefront controller for the MMT NGS-AO system. © 2010 SPIE.


Bendek E.A.,University of Arizona | Hart M.,University of Arizona | Powell K.B.,MMT Observatory | Vaitheeswaran V.,University of Arizona | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

Laser tomography capability using a multi laser guide star (LGS) system is being implemented at the 6.5 m MMT telescope on Mt. Hopkins, AZ. The system uses five range-gated and dynamically refocused Rayleigh laser beacons to sense the atmospheric wavefront aberration. Corrections are then applied to the wavefront using the 336-actuator adaptive secondary mirror of the telescope. So far, the system has demonstrated successful control of ground-layer aberration over a field of view substantially wider than is delivered by conventional adaptive optics. In this paper, we report the latest results from this mode of operation, using for the first time a plate scale on our IR science camera that samples the diffraction scale at the Nyquist limit. We also discuss findings for a reduction in the width of the on-axis point-spread function from 1.07" to <0.2" in H band and present the progress achieved toward the implementation of laser tomography. This will be attempted by means of a least squares reconstructor, which is obtained using simultaneous measurements of the wavefronts from the LGS and an additional natural guide star. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).


Hastie M.,MMT Observatory | Williams G.G.,MMT Observatory
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

In the ten years since the converted 6.5m MMT was dedicated the observatory has built up an impressive suite of instrumentation to compliment the three interchangeable secondary mirrors. This review paper presents an up-to-date perspective on all the capabilities of our full range of instrumentation, highlighting newly commissioned instruments (the MMT and Magellan InfraRed Spectrograph (MMIRS), an infrared spectrograph) and new modes or upgrades for established instruments (such as; Red Channel, the MMT's workhorse spectrograph, Hectochelle, an optical fiber-fed, multi-object spectrograph and the AO instruments CLIO, a 5 micron camera and BLINC, a mid-infrared camera). The MMT's pioneering adaptive secondary mirror can be used with both natural guide stars (NGS) or with a Rayleigh laser guide star (LGS) system. The LGS has recently demonstrated wide-field partial compensation with ground layer adaptive optics and here we present progress to date. Finally, we report on the start of a project to investigate how the instrument suite has contributed to the science productivity the MMT over the last 10 years. © 2010 Copyright SPIE - The International Society for Optical Engineering.


Bilinski C.,University of Arizona | Smith N.,University of Arizona | Li W.,University of California at Berkeley | Grant Williams G.,MMT Observatory | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

We searched through roughly 12 years of archival survey data acquired by the Katzman Automatic Imaging Telescope (KAIT) as part of the Lick Observatory Supernova Search in order to detect or place limits on possible progenitor outbursts of Type IIn supernovae (SNe IIn). The KAIT data base contains multiple pre-SN images for five SNe IIn (plus one ambiguous case of an SN IIn/imposter) within 50 Mpc. No progenitor outbursts are found using the false discovery rate statistical method in any of our targets. Instead, we derive limiting magnitudes (LMs) at the locations of the SNe. These LMs (typically reaching mR ≈ 19.5mag) are compared to outbursts of SN 2009ip and η Car, plus additional simulated outbursts. We find that the data for SN 1999el and SN 2003dv are of sufficient quality to rule out events ~40 d before the main peak caused by initially faint SNe from blue supergiant precursor stars, as in the cases of SN 2009ip and SN 2010mc. These SNe IIn may thus have arisen from red supergiant progenitors, or they may have had a more rapid onset of circumstellar matter interaction. We also estimate the probability of detecting at least one outburst in our data set to be ≳60% for each type of the example outbursts, so the lack of any detections suggests that such outbursts are either typically less luminous (intrinsically or owing to dust) than ~-13 mag, or not very common among SNe IIn within a few years prior to explosion. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Vilas F.,MMT Observatory | Vilas F.,Planetary Science Institute | Hendrix A.R.,Planetary Science Institute | Hendrix A.R.,Jet Propulsion Laboratory
Astronomical Journal | Year: 2015

Evidence for the manifestation of space weathering in S-complex asteroids as a bluing of the UV/blue reflectance spectrum is extended using high resolution CCD reflectance spectra of 21 main-belt, 1 Mars-crossing, and 3 near-Earth asteroids covering a wavelength range of 320-620 nm. Demonstration of the transition of iron-bearing materials from volume scattering to surface (Fresnel) scattering is apparent as an abrupt downturn at wavelengths just short of 400 nm in reflectance spectra of fresh asteroid surfaces. The weathering away of this downturn is demonstrated by its absence in reflectance spectra of mature S-complex asteroids, consistent with an increase in npFe0 on the material's surface. Modeling of the effects of the addition of small amounts of npFe0 to particles from both a hypothetical mineral and a terrestrial basalt shows that evidence of the addition of 0.0001% npFe0 affects the reflectance at UV/blue wavelengths, while the addition of 0.01% is required to see the visible/near-infrared reddening and diminution of absorption features. Thus, the UV/blue reflectance characteristics allow earlier detection of the onset of space weathering effects. Combining UV/blue spectral characteristics of asteroids and ordinary chondrite meteorites with estimated ages of the young Datura family, we establish a method of dating asteroid surface ages during the early stages of space weathering. We demonstrate by dating the surface of NEA 163249 2002 GT to be 109 (±18) to 128 (±10) Kyr. © 2015. The American Astronomical Society. All rights reserved..

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