868 research outputs found
Volatile Composition and Outgassing in C/2018 Y1 (IWAMOTO): Extending Detection Limits for High-Resolution IR Cometary Spectroscopy at the NASA-IRTF
We used iSHELL, the powerful high-resolution ( /~ 40,000) cross-dispersed IR spectrograph at the NASA-IRTF to measure the native ice composition and outgassing of moderately bright, long-period comet C/2018 Y1 (Iwamoto) (hereafter Y1) within weeks of its discovery. We measured production rates for H2O, and production rates and abundance ratios relative to H2O for eight trace molecules, including the most complete measure of cometary CH4 achieved to date. Compared with mean abundances measured among comets, our study revealed enriched CH3OH and C2H6 yet depleted CO and C2H2, perhaps indicating highly efficient H- atom addition on interstellar grains prior to their incorporation into the nucleus. The combined high spectral resolving power and broad spectral coverage of iSHELL allowed characterizing cometary composition using only three instrument settings, and its long-slit coverage allowed comparing the spatial distributions of molecular emissions and dust continuum
Line Evolution of the Nova V5587 Sgr from Early to Nebula Phase
The spectral evolution of the nova V5587 Sgr has been monitored at Koyama Astronomical Observatory and Higashi-Hiroshima Observatory, Japan, from the early to nebula phase. The nova rebrightened several times. The spectra during the early phase showed emission lines of H α, H β, O I, He I, He II, N II, Fe II. Nova V5587 Sgr is classified into the Fe II type. The helium abundance of the nova is estimated as N(He)/N(H) = 0.134 ± 0.09. The light curve, the spectral evolution, and the helium abundance in V5587 Sgr are similar to those of the nova PW Vul
Spectroscopic Monitoring Observations of Nova V1724 Aql in 2012
Spectroscopic and photometric monitoring observations of nova Apl 2012 (V1724 Apl) were conducted at Koyama Astronomical Observatory, Fujii-Kurosaki Observatory and Bisei Astronomical Observatory. The nova was initially considered as an outbursting pre-main-sequence young stellar object. Our monitoring observations have revealed the nova to be a Fe II type classical nova. The temporal evolution of spectra and light curves of the nova were similar to those of a slow nova (e.g., V1280 Sco and V5558 Sgr). We observed no evidence of molecule formation in V1724 Aql in contrast with V2676 Oph in which dust formation occurred after the molecular formation in the nova outflow
Detection of Diatomic Molecules in the Dust Forming Nova V2676 Oph
Novae are generally considered to be hot astronomical objects and show effective temperatures up to 10,000 K or higher at their visual maximum. But, it is theoretically predicted that the outer envelope of the nova outflow can become cool enough to form molecules that would be dissociated at high temperatures. We detected strong absorption bands of C2 and CN radicals in the optical spectrum of Nova V2676 Oph, a very slow nova with dust formation. This is the first report of the detection of C2 and the second one of CN in novae during outburst. Although such simple molecules are predicted to form in the envelope of the outflow based on previous studies, there are few reports of their detection. In the case of V2676 Oph, the presence of the molecular envelope is considered to be very transient, lasting several days only
Liquid-like thermal conduction in a crystalline solid
A solid conducts heat through both transverse and longitudinal acoustic
phonons, but a liquid employs only longitudinal vibrations. Here, we report
that the crystalline solid AgCrSe2 has liquid-like thermal conduction. In this
compound, Ag atoms exhibit a dynamic duality that they are exclusively involved
in intense low-lying transverse acoustic phonons while they also undergo local
fluctuations inherent in an order-to-disorder transition occurring at 450 K. As
a consequence of this extreme disorder-phonon coupling, transverse acoustic
phonons become damped as approaching the transition temperature, above which
they are not defined anymore because their lifetime is shorter than the
relaxation time of local fluctuations. Nevertheless, the damped longitudinal
acoustic phonon survives for thermal transport. This microscopic insight might
reshape the fundamental idea on thermal transport properties of matter and
facilitates the optimization of thermoelectrics.Comment: four figures, supplemental informatio
Chandra Observations of Type Ia Supernovae: Upper Limits to the X-ray Flux of SN 2002bo, SN 2002ic, SN 2005gj, and SN 2005ke
We set sensitive upper limits to the X-ray emission of four Type Ia
supernovae (SNe Ia) using the Chandra X-ray Observatory. SN 2002bo, a normal,
although reddened, nearby SN Ia, was observed 9.3 days after explosion. For an
absorbed, high temperature bremsstrahlung model the flux limits are 3.2E-16
ergs/cm^2/s (0.5-2 keV band) and 4.1E-15 ergs/cm^2/s (2-10 keV band). Using
conservative model assumptions and a 10 km/s wind speed, we derive a mass loss
rate of \dot{M} ~ 2E-5 M_\odot/yr, which is comparable to limits set by the
non-detection of Halpha lines from other SNe Ia. Two other objects, SN 2002ic
and SN 2005gj, observed 260 and 80 days after explosion, respectively, are the
only SNe Ia showing evidence for circumstellar interaction. The SN 2002ic X-ray
flux upper limits are ~4 times below predictions of the interaction model
currently favored to explain the bright optical emission. To resolve this
discrepancy we invoke the mixing of cool dense ejecta fragments into the
forward shock region, which produces increased X-ray absorption. A modest
amount of mixing allows us to accommodate the Chandra upper limit. SN 2005gj is
less well studied at this time. Assuming the same circumstellar environment as
for SN 2002i, the X-ray flux upper limits for SN 2005gj are ~4 times below the
predictions, suggesting that mixing of cool ejecta into the forward shock has
also occurred here. Our reanalysis of Swift and Chandra data on SN 2005ke does
not confirm a previously reported X-ray detection. The host galaxies NGC 3190
(SN 2002bo) and NGC 1371 (SN 2005ke) each harbor a low luminosity (L_X ~ 3-4E40
ergs/s) active nucleus in addition to wide-spread diffuse soft X-ray emission.Comment: 16 pages, to appear in ApJ (20 Nov 2007
Recent Searches for the Radio Lines of NH_3 in Comets
Radio observations in the ammonia inversion lines of four comets, C/2001 A2
(LINEAR), 153P/Ikeya-Zhang, C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR), were
performed at the Effelsberg 100-m Radio Telescope during their respective close
approaches to Earth. None of the four lowest energy metastable lines
(J,K=J),J=1--4, could be detected in these comets. We derive the following 3
sigma upper bounds on the NH_3 production rate, and c omparing to the
corresponding water production rates, percentage NH_3 abundances relative to
H_2O:
Q(NH_3) < 1.9x10^26 s^-1 (0.63%) for C/2001 A2 (LINEAR),
Q(NH_3) < 2.7x10^26 s^-1 (0.13%) for C/2001 Q4 (NEAT),
Q(NH_3) < 2.3x10^27 s^-1 (0.74%) for C/2002 T7 (LINEAR) and Q(NH_3) <=
6.3x10^26 s^-1 (0.63%) for Comet 153P/Ikeya-Zhang.
At 0.74% or less, the ammonia-to-water ratios are factors of 2 below the
value for C/1995 O1 (Hale-Bopp) and 1P/Halley, suggesting chemical diversity
between comets. The 18-cm lines of OH were clearly detected in the two comets
observed during the 2004 campaign, thereby validating the cometary ephemerides.Comment: 8 pages, 3 figure
The rotation and coma profiles of comet C/2004 Q2 (Machholz)
Aims. Rotation periods of cometary nuclei are scarce, though important when
studying the nature and origin of these objects. Our aim is to derive a
rotation period for the nucleus of comet C/2004 Q2 (Machholz). Methods. C/2004
Q2 (Machholz) was monitored using the Merope CCD camera on the Mercator
telescope at La Palma, Spain, in January 2005, during its closest approach to
Earth, implying a high spatial resolution (50km per pixel). One hundred seventy
images were recorded in three different photometric broadband filters, two blue
ones (Geneva U and B) and one red (Cousins I). Magnitudes for the comet's
optocentre were derived with very small apertures to isolate the contribution
of the nucleus to the bright coma, including correction for the seeing. Our CCD
photometry also permitted us to study the coma profile of the inner coma in the
different bands. Results. A rotation period for the nucleus of P = 9.1 +/- 0.2
h was derived. The period is on the short side compared to published periods of
other comets, but still shorter periods are known. Nevertheless, comparing our
results with images obtained in the narrowband CN filter, the possibility that
our method sampled P/2 instead of P cannot be excluded. Coma profiles are also
presented, and a terminal ejection velocity of the grains v_gr = 1609 +/- 48
m/s is found from the continuum profile in the I band.Comment: 11 pages, 9 figures, accepted by A&
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