45 research outputs found
The 2000 outburst of the recurrent nova CI Aquilae: optical spectroscopy
We present low- and medium resolution spectra of the recurrent nova CI
Aquilae taken at 14 epochs in May and June, 2000. The overall appearance is
similar to other U Sco-type recurrent novae (U Sco, V394 CrA). Medium
resolution (R=7000-10000) hydrogen and iron profiles suggest an early expansion
velocity of 2000-2500 km/s. The H\alpha evolution is followed from Dt = -0.6 d
to +53 d, starting from a nearly Gaussian shape to a double peaked profile
through strong P-Cyg profiles. The interstellar component of the sodium D line
and two diffuse interstellar bands put constraints on the interstellar
reddening which is estimated to be E(B-V)=0.85\pm0.3. The available visual and
CCD-V observations are used to determine t0,t2 and t3. The resulting parameters
are: t0=2451669.5\pm0.1, t2=30\pm1 d, t3=36\pm1 d. The recent lightcurve is
found to be generally similar to that observed in 1917 with departures as large
as 1-2 mag in certain phases. This behaviour is also typical for the U Sco
subclass.Comment: 8 pages, 7 figures, accepted for publication in A&
A Prediction Formula of Supersoft X-ray Phase of Classical Novae
On the basis of the recently developed universal decline law of classical
novae, we propose prediction formulae for supersoft X-ray on and off times,
i.e., t_{X-on} = (10 \pm 1.8) t_3 days and t_{X-off} = (5.3 \pm 1.4)
(t_3)^{1.5} days for 8 < t_3 < 80 days. We have determined the absolute
magnitude of our free-free emission model light curves and derived maximum
magnitude vs. rate of decline (MMRD) relations. Our theoretical MMRD relations
are governed by two parameters, one is the white dwarf (WD) mass and the other
is the initial envelope mass at a nova outburst; this second parameter explains
the scatter of MMRD points of individual novae. Our theoretical MMRD relations
are also in good agreement with the well-known empirical formulae. We also show
another empirical relation of M_V(15) ~ -5.7 \pm 0.3 based on the absolute
magnitude of our model light curves, i.e., the absolute magnitude at 15 days
after optical maximum is almost common among various novae. We analyzed ten
nova light curves, in which a supersoft X-ray phase was detected, and estimated
their WD masses. The models best reproducing simultaneously the optical and
supersoft X-ray observations are ONeMg WDs with 1.28 \pm 0.04 M_\sun (V598
Pup), 1.23 \pm 0.05 M_\sun (V382 Vel), 1.15 \pm 0.06 M_\sun (V4743 Sgr), 1.13
\pm 0.06 M_\sun (V1281 Sco), 1.2 \pm 0.05 M_\sun (V597 Pup), 1.06 \pm 0.07
M_\sun (V1494 Aql), 1.04 \pm 0.07 M_\sun (V2467 Cyg), 1.07 \pm 0.07 M_\sun
(V5116 Sgr), 1.05 \pm 0.05 M_\sun (V574 Pup), and a CO WD with 0.93 \pm 0.08
M_\sun (V458 Vul). The newly proposed relationships are consistent with the
emergence or decay epoch of the supersoft X-ray phase of these ten novae.
Finally, we discuss the mechanism of shock-origin hard X-ray component in
relation to the emergence of companion star from the WD envelope.Comment: 36 pages, 29 figures, to appear in the Astrophysical Journa
Detection of Near-IR CO Absorption Bands in R Coronae Borealis Stars
R Coronae Borealis (RCB) stars are hydrogen-deficient, carbon-rich pulsating
post-AGB stars that experience massive irregular declines in brightness caused
by circumstellar dust formation. The mechanism of dust formation around RCB
stars is not well understood. It has been proposed that CO molecules play an
important role in cooling the circumstellar gas so that dust may form. We
report on a survey for CO in a sample of RCB stars. We obtained H- and K-band
spectra including the first and second overtone CO bands for eight RCB stars,
the RCB-like star, DY Per and the final-helium-flash star, FG Sge. The first
and second overtone CO bands were detected in the cooler (T(eff)<6000 K) RCB
stars, Z Umi, ES Aql, SV Sge and DY Per. The bands are not present in the
warmer (T(eff)>6000 K) RCB stars, R CrB, RY Sgr, SU Tau, XX Cam. In addition,
first overtone bands are seen in FG Sge, a final-helium-flash star that is in
an RCB-like phase at present. Effective temperatures of the eight RCB stars
range from 4000 to 7250 K. The observed photospheric CO absorption bands were
compared to line-blanketed model spectra of RCB stars. As predicted by the
models, the CO bands are strongest in the coolest RCB stars and not present in
the warmest. No correlation was found between the presence or strength of the
CO bands and dust formation activity in the stars.Comment: 13 oages, 3 figures, AJ in pres
Elemental Abundances in the Ejecta of Old Classical Novae from Late-Epoch Spitzer Spectra
We present Spitzer Space Telescope mid-infrared IRS spectra, supplemented by
ground-based optical observations, of the classical novae V1974 Cyg, V382 Vel,
and V1494 Aql more than 11, 8, and 4 years after outburst respectively. The
spectra are dominated by forbidden emission from neon and oxygen, though in
some cases, there are weak signatures of magnesium, sulfur, and argon. We
investigate the geometry and distribution of the late time ejecta by
examination of the emission line profiles. Using nebular analysis in the low
density regime, we estimate lower limits on the abundances in these novae. In
V1974 Cyg and V382 Vel, our observations confirm the abundance estimates
presented by other authors and support the claims that these eruptions occurred
on ONe white dwarfs. We report the first detection of neon emission in V1494
Aql and show that the system most likely contains a CO white dwarf.Comment: 22 pages, 12 figure
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Bij problemen op het gebied van natuur en milieu, duurzaamheid en voedselketens liggen oorzaken en gevolgen per definitie op verschillende schaalniveaus, van lokaal tot de wereld, van korte tot lange termijn. Binnen het thema Scaling and Governance worden manieren ontwikkeld om ondanks die complexiteit toch tot effectief beleid te kunnen komen
The unusual Nova Cygni 2006 (V2362 Cyg)
Context: Optical nova lightcurves often have structures, such as rapid
declines and recoveries, due to nebular or dusty phases of the ejecta. Nova
Cygni 2006 (V2362 Cyg) underwent an unusual brightening after an early rapid
decline. The shape of the lightcurve can be compared to that of V1493 Aql, but
the whole event in that case was not as bright and only lasted a couple of
weeks. V2362 Cyg had a moderately fast decline of t_2 = 9.0 before
rebrightening, which lasted 250 days after maximum. Aims: We present an
analysis of our own spectroscopic investigations in combination with AAVSO
photometric data covering the whole rebrightening phase until the return to the
final decline. Methods: We used the medium resolution spectroscopy obtained in
ten nights over a period of 79 nights to investigate the change of the velocity
structure of the ejecta. The publicly available AAVSO photometry was used to
analyze the overall properties and the energy of the brightening. Results:
Although the behavior of the main outburst (velocity, outburst magnitude, and
decline timescales) resembles a ``normal'' classical nova, the shell clearly
underwent a second fast mass ejecting phase, causing the unusual properties.
The integrated flux during this event contributes ~ 40 % to the total radiation
energy of the outburst. The evolution of the H_alpha profile during the bump
event is obtained by subtracting the emission of the detached shells of the
main eruption by a simple optically thin model. A distance of D ~ 7.5
{+3.0}{-2.5} kpc and an interstellar extinction E(B-V) = 0.6 +/- 0.1 was also
derived.Comment: 4 pages, 4 Postscript figures, accepted for A&A Letter
Visible and Near-Infrared Spectrophotometry of the Deep Impact Ejecta of Comet 9P/Tempel 1
We have obtained optical spectrophotometry of the evolution of comet
9P/Tempel 1 after the impact of the Deep Impact probe, using the Supernova
Integral Field Spectrograph (SNIFS) at the UH 2.2m telescope, as well as
simultaneous optical and infrared spectra using the Lick
Visible-to-Near-Infrared Imaging Spectrograph (VNIRIS) spectrograph. The
spatial distribution and temporal evolution of the "violet band" CN (0-0)
emission and of the 630 nm [OI] emission was studied. We found that CN emission
centered on the nucleus increased in the two hours after impact, but that this
CN emission was delayed compared to the light curve of dust-scattered sunlight.
The CN emission also expanded faster than the cloud of scattering dust. The
emission of [OI] at 630 nm rose similarly to the scattered light, but then
remained nearly constant for several hours after impact. On the day following
the impact, both CN and [OI] emission concentrated on the comet nucleus had
returned nearly to pre-impact levels. We have also searched for differences in
the scattering properties of the dust ejected by the impact compared to the
dust released under normal conditions. Compared to the pre-impact state of the
comet, we find evidence that the color of the comet was slightly bluer during
the post-impact rise in brightness. Long after the impact, in the following
nights, the comet colors returned to their pre-impact values. This can be
explained by postulating a change to a smaller particle size distribution in
the ejecta cloud, in agreement with the findings from mid-infrared observatons,
or by postulating a large fraction of clean ice particles, or by a combination
of these two.Comment: 28 pages of text and 8 figures. Paper is accepted for publication in
Icaru
Increased SIRT3 combined with PARP inhibition rescues motor function of SBMA mice.
Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disease with substantial mitochondrial and metabolic dysfunctions. SBMA is caused by polyglutamine (polyQ) expansion in the androgen receptor (AR). Activating or increasing the NAD+-dependent deacetylase, SIRT3, reduced oxidative stress and death of cells modeling SBMA. However, increasing diminished SIRT3 in AR100Q mice failed to reduce acetylation of the SIRT3 target/antioxidant, SOD2, and had no effect on increased total acetylated peptides in quadriceps. Yet, overexpressing SIRT3 resulted in a trend of motor recovery, and corrected TCA cycle activity by decreasing acetylation of SIRT3 target proteins. We sought to boost blunted SIRT3 activity by replenishing diminished NAD+ with PARP inhibition. Although NAD+ was not affected, overexpressing SIRT3 with PARP inhibition fully restored hexokinase activity, correcting the glycolytic pathway in AR100Q quadriceps, and rescued motor endurance of SBMA mice. These data demonstrate that targeting metabolic anomalies can restore motor function downstream of polyQ-expanded AR