| 1. |
- Abazov, V. M., et al.
(författare)
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The upgraded DO detector
- 2006
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 565:2, s. 463-537
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Tidskriftsartikel (refereegranskat)abstract
- The DO experiment enjoyed a very successful data-collection run at the Fermilab Tevatron collider between 1992 and 1996. Since then, the detector has been upgraded to take advantage of improvements to the Tevatron and to enhance its physics capabilities. We describe the new elements of the detector, including the silicon microstrip tracker, central fiber tracker, solenoidal magnet, preshower detectors, forward muon detector, and forward proton detector. The uranium/liquid -argon calorimeters and central muon detector, remaining from Run 1, are discussed briefly. We also present the associated electronics, triggering, and data acquisition systems, along with the design and implementation of software specific to DO.
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| 2. |
- Abazov, V. M., et al.
(författare)
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Determination of the strong coupling constant from the inclusive jet cross section in pp collisions at s=1.96 TeV
- 2009
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Ingår i: PHYS REV D. - 1550-7998 .- 1550-2368. ; 80, s. 111107-
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Tidskriftsartikel (refereegranskat)abstract
- We determine the strong coupling constant alpha(s) and its energy dependence from the p(T) dependence of the inclusive jet cross section in pp collisions at s=1.96 TeV. The strong coupling constant is determined over the transverse momentum range 50 < p(T)< 145 GeV. Using perturbative QCD calculations to order O(alpha(3)(s)) combined with O(alpha(4)(s)) contributions from threshold corrections, we obtain alpha(s)(M-Z)=0.1161(-0.0048)(+0.0041). This is the most precise result obtained at a hadron-hadron collider.
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| 3. |
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| 4. |
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| 5. |
- Berger, E., et al.
(författare)
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An Intermediate Luminosity Transient in NGC 300 : The Eruption of a Dust-Enshrouded Massive Star
- 2009
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 699, s. 1850-1865
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Tidskriftsartikel (refereegranskat)abstract
- We present multi-epoch high-resolution optical spectroscopy, UV/radio/X-ray imaging, and archival Hubble and Spitzer observations of an intermediate luminosity optical transient recently discovered in the nearby galaxy NGC 300. We find that the transient (NGC 300 OT2008-1) has a peak absolute magnitude of M bol ≈ -11.8 mag, intermediate between novae and supernovae, and similar to the recent events M85 OT2006-1 and SN 2008S. Our high-resolution spectra, the first for this event, are dominated by intermediate velocity (~200-1000 km s-1) hydrogen Balmer lines and Ca II emission and absorption lines that point to a complex circumstellar environment, reminiscent of the yellow hypergiant IRC+10420. In particular, we detect asymmetric Ca II H&K absorption with a broad red wing extending to ~103 km s-1, indicative of gas inflow at high velocity (possibly the wind of a massive binary companion). The low luminosity, intermediate velocities, and overall similarity to a known eruptive star indicate that the event did not result in a complete disruption of the progenitor. We identify the progenitor in archival Spitzer observations, with deep upper limits from Hubble data. The spectral energy distribution points to a dust-enshrouded star with a luminosity of about 6 × 104 L sun, indicative of a ~10-20 M sun progenitor (or binary system). This conclusion is in good agreement with our interpretation of the outburst and circumstellar properties. The lack of significant extinction in the transient spectrum indicates that the dust surrounding the progenitor was cleared by the outburst. We thus predict that the progenitor should be eventually visible with Hubble if the transient event marks an evolutionary transition to a dust-free state, or with Spitzer if the event marks a cyclical process of dust formation.
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| 6. |
- Clocchiatti, Alejandro, et al.
(författare)
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Late-time HST photometry of SN1994I : Hints of positron annihilation energy deposition
- 2008
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 120:865, s. 290-300
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Tidskriftsartikel (refereegranskat)abstract
- We present multicolor Hubble Space Telescope ( HST) WFPC2 broadband observations of the Type Ic SN 1994I obtained similar to 280 d after maximum light. We measure the brightness of the SN and, relying on the detailed spectroscopic database of SN 1994I, we transform the ground-based photometry obtained at early times to the HST photometric system, deriving light curves for the WFPC2 F439W, F555W, F675W, and F814W passbands that extend from 7 days before to 280 days after maximum. We use the multicolor photometry to build a quasi-bolometric light curve of SN 1994I, and compare it with similarly constructed light curves of other supernovae. In doing so, we propose and test a scaling in energy and time that allows for a more meaningful comparison of the exponential tails of different events. Through comparison with models, we find that the late-time light curve of SN 1994I is consistent with that of spherically symmetric ejecta in homologous expansion, for which the ability to trap the gamma-rays produced by the radioactive decay of Co-56 diminishes roughly as the inverse of time squared. We also find that by the time of the HST photometry, the light curve was significantly energized by the annihilation of positrons.
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| 7. |
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| 8. |
- Graves, Genevieve J. M., et al.
(författare)
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Limits from the Hubble Space Telescope on a Point Source in SN 1987A
- 2005
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 629, s. 944-959
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Tidskriftsartikel (refereegranskat)abstract
- We observed supernova 1987A (SN 1987A) with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) in 1999 September and again with the Advanced Camera for Surveys (ACS) on the HST in 2003 November. Our spectral observations cover ultraviolet (UV) and optical wavelengths from 1140 to 10266 Å, and our imaging observations cover UV and optical wavelengths from 2900 to 9650 Å. No point source is observed in the remnant. We obtain a limiting flux of Fopt<=1.6×10-14 ergs s-1 cm-2 in the wavelength range 2900-9650 Å for any continuum emitter at the center of the supernova remnant (SNR). This corresponds to an intrinsic luminosity of Lopt<=5×1033 ergs s-1. It is likely that the SNR contains opaque dust that absorbs UV and optical emission, resulting in an attenuation of ~35% due to dust absorption in the SNR. Correcting for this level of dust absorption would increase our upper limit on the luminosity of a continuum source by a factor of 1.54. Taking into account dust absorption in the remnant, we find a limit of Lopt<=8×1033 ergs s-1. We compare this upper bound with empirical evidence from point sources in other supernova remnants and with theoretical models for possible compact sources. We show that any survivor of a possible binary system must be no more luminous than an F6 main-sequence star. Bright young pulsars such as Kes 75 or the Crab pulsar are excluded by optical and X-ray limits on SN 1987A. Other nonplerionic X-ray point sources have luminosities similar to the limits on a point source in SN 1987A; RCW 103 and Cas A are slightly brighter than the limits on SN 1987A, while Pup A is slightly fainter. Of the young pulsars known to be associated with SNRs, those with ages <=5000 yr are all too bright in X-rays to be compatible with the limits on SN 1987A. Examining theoretical models for accretion onto a compact object, we find that spherical accretion onto a neutron star is firmly ruled out and that spherical accretion onto a black hole is possible only if there is a larger amount of dust absorption in the remnant than predicted. In the case of thin-disk accretion, our flux limit requires a small disk, no larger than 1010 cm, with an accretion rate no more than 0.3 times the Eddington accretion rate. Possible ways to hide a surviving compact object include the removal of all surrounding material at early times by a photon-driven wind, a small accretion disk, or very high levels of dust absorption in the remnant. It will not be easy to improve substantially on our optical-UV limit for a point source in SN 1987A, although we can hope that a better understanding of the thermal infrared emission will provide a more complete picture of the possible energy sources at the center of SN 1987A.
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| 9. |
- Gröningsson, Per, et al.
(författare)
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Coronal emission from the shocked circumstellar ring of SN 1987A
- 2006
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 456:2, s. 581-589
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Tidskriftsartikel (refereegranskat)abstract
- High resolution spectra with UVES/VLT of SN 1987A from December 2000 until November 2005 show a number of high ionization lines from gas with velocities of ± 350 km s-1, emerging from the shocked gas formed by the ejecta-ring collision. These include coronal lines from [Fe X], [Fe XI] and [Fe XIV] which have increased by a factor of 20 during the observed period. The evolution of the lines is similar to that of the soft X-rays, indicating that they arise in the same component. The line ratios are consistent with those expected from radiative shocks with velocity 310{-}390 km s-1, corresponding to a shock temperature of (1.6{-}2.5)× 106 K. A fraction of the coronal emission may, however, originate in higher velocity adiabatic shocks.
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| 10. |
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