210 research outputs found
Twelve type II-P supernovae seen with the eyes of Spitzer
Core-collapse supernovae (CC SNe), especially those of type II-plateau
(II-P), are thought to be important contributors to cosmic dust production. The
most obvious indicator of the presence of newly-formed and/or pre-existing dust
is the time-dependent mid-infrared (MIR) excess coming from the environment of
SNe. Our goal was to collect publicly available, previously unpublished
measurements on type II-P (or peculiar IIP) SNe from the Spitzer database. The
temporal changes of the observed fluxes may be indicative of the underlying
supernova, while spectral energy distribution (SED) fitting to the fluxes in
different IRAC channels may reveal the physical parameters of the mid-IR
radiation, presumably due to warm dust. IRS spectra were extracted and
calibrated with SPICE, while photometric SEDs were assembled using IRAF and
MOPEX. Calculated SEDs from observed fluxes were fit with simple dust models to
get basic information on the dust presumed as the source of MIR radiation. We
found twelve SNe satisfying the criterion above, observed at late-time epochs
(typically after +300 days). In three cases we could not identify any point
source at the SN position on late time IRAC images. We found two SNe, 2005ad
and 2005af, which likely have newly-formed dust in their environment, while in
the other seven cases the observed MIR flux may originate from pre-existing
circumstellar or interstellar dust. Our results support the previous
observational conclusions that warm new dust in the environment of SNe
contributes only marginally to cosmic dust content.Comment: Accepted for publication in Astronomy and Astrophysics; 15 pages, 8
figures, 9 tables (Ver. 2.: language edited version, minor corrections were
made in the title, in the text, and in the reference list
Mass and orbit constraints of the gamma-ray binary LS 5039
We present the results of space-based photometric and ground-based
spectroscopic observing campaigns on the gamma-ray binary LS 5039. The new
orbital and physical parameters of the system are similar to former results,
except we found a lower eccentricity. Our MOST-data show that any broad-band
optical photometric variability at the orbital period is below the 2 mmag
level. Light curve simulations support the lower value of eccentricity and
imply that the mass of the compact object is higher than 1.8 solar masses.Comment: 2 pages, 1 figure (with 2 panels); to be published in the
Proceedings: From Interacting Binaries to Exoplanets: Essential Modeling
Tools, IAU Symposium 282 (18-22 July, 2011, Tatranska Lomnica, Slovakia
Measuring Expansion Velocities in Type II-P Supernovae
We estimate photospheric velocities of Type II-P supernovae using model
spectra created with SYNOW, and compare the results with those obtained by more
conventional techniques, such as cross-correlation, or measuring the absorption
minimum of P Cygni features. Based on a sample of 81 observed spectra of 5 SNe,
we show that SYNOW provides velocities that are similar to ones obtained by
more sophisticated NLTE modeling codes, but they can be derived in a less
computation-intensive way. The estimated photospheric velocities (v_model) are
compared to ones measured from Doppler-shifts of the absorption minima of the
Hbeta and the FeII \lambda5169 features.
Our results confirm that the FeII velocities (v_Fe) have tighter and more
homogeneous correlation with the estimated photospheric velocities than the
ones measured from Hbeta, but both suffer from phase-dependent systematic
deviations from those. The same is true for comparison with the
cross-correlation velocities. We verify and improve the relations between v_Fe,
v_Hbeta and v_model in order to provide useful formulae for
interpolating/extrapolating the velocity curves of Type II-P SNe to phases not
covered by observations. We also discuss the implications of our results for
the distance measurements of Type II-P SNe, and show that the application of
the model velocities is preferred in the Expanding Photosphere Method.Comment: 19 pages, 10 figures, accepted in MNRA
The contact binary VW Cephei revisited: surface activity and period variation
Context. Despite the fact that VW Cephei is one of the well-studied contact
binaries in the literature, there is no fully consistent model available that
can explain every observed property of this system.
Aims. Our motivation is to obtain new spectra along with photometric
measurements, to analyze what kind of changes may have happened in the system
in the past two decades, and to propose new ideas for explaining them.
Methods. For the period analysis we determined 10 new times of minima from
our light curves, and constructed a new OC diagram of the system. Radial
velocities of the components were determined using the cross-correlation
technique. The light curves and radial velocities were modelled simultaneously
with the PHOEBE code. All observed spectra were compared to synthetic spectra
and equivalent widths of the H line were measured on their differences.
Results. We have re-determined the physical parameters of the system
according to our new light curve and spectral models. We confirm that the
primary component is more active than the secondary, and there is a correlation
between spottedness and the chromospheric activity. We propose that flip-flop
phenomenon occurring on the primary component could be a possible explanation
of the observed nature of the activity. To explain the period variation of VW
Cep, we test two previously suggested scenarios: presence of a fourth body in
the system, and the Applegate-mechanism caused by periodic magnetic activity.
We conclude that although none of these mechanisms can be ruled out entirely,
the available data suggest that mass transfer with a slowly decreasing rate
gives the most likely explanation for the period variation of VW Cep.Comment: 13 pages, 18 figures, 9 tables, accepted for publication in Astronomy
and Astrophysic
The Unusually Luminous Extragalactic Nova SN 2010U
We present observations of the unusual optical transient SN 2010U, including
spectra taken 1.03 days to 15.3 days after maximum light that identify it as a
fast and luminous Fe II type nova. Our multi-band light curve traces the fast
decline (t_2 = 3.5 days) from maximum light (M_V = -10.2 mag), placing SN 2010U
in the top 0.5% of the most luminous novae ever observed. We find typical
ejecta velocities of approximately 1100 km/s and that SN 2010U shares many
spectral and photometric characteristics with two other fast and luminous Fe II
type novae, including Nova LMC 1991 and M31N-2007-11d. For the extreme
luminosity of this nova, the maximum magnitude vs. rate of decline relationship
indicates a massive white dwarf progenitor with a low pre-outburst accretion
rate. However, this prediction is in conflict with emerging theories of nova
populations, which predict that luminous novae from massive white dwarfs should
preferentially exhibit an alternate spectral type (He/N) near maximum light.Comment: 16 pages, 16 figures. Submitted to the Astrophysical Journa
The Peculiar Type Ia Supernova 1999by: Spectroscopy at Early Epochs
We present medium resolution (lambda/Delta lambda = 2500) optical
spectroscopy of SN 1999by in NGC 2841 made around its light maximum. The depth
ratio of the two Si II features at 5800 AA and 6150 AA being R(SiII) approx.
0.63 at maximum indicates that this SN belongs to the peculiar, sub-luminous
SNe Ia. Radial velocities inferred from the minimum of the 6150 AA trough
reveal a steeper decline of the velocity curve than expected for ``normal'' SNe
Ia, consistent with the behavior of published VRI light curves. A revised
absolute magnitude of SN 1999by and distance to its host galaxy NGC 2841 is
estimated based on the Multi-Color Light Curve Shape (MLCS) method, resulting
in M_V(max)=-18.06+/- 0.1 mag and d = 17.1+/-1.2 Mpc, respectively. An
approximative linear dependence of the luminosity parameter Delta on R(SiII) is
presented.Comment: accepted for publication in Astron. Journal (2001 June
Distance to the Active Galaxy NGC 6951 via the Type Ia Supernova 2000E
CCD-photometry and low-resolution spectroscopy of the bright supernova SN
2000E in NGC 6951 are presented. Both the light curve extending up to 150 days
past maximum and the spectra obtained at 1 month past maximum confirm that SN
2000E is of Type Ia. The reddening of SN 2000E is determined as
E(B-V)=0.36+/-0.15, its error is mainly due to uncertainties in the predicted
SN (B-V) colour at late epochs. The V(RI)_C light curves are analyzed with the
Multi-Colour Light Curve Shape (MLCS) method. The shape of the late light curve
suggests that SN 2000E was overluminous by about 0.5 mag at maximum comparing
with a fiducial SN Ia. This results in an updated distance of 33+/-8 Mpc of NGC
6951 (corrected for interstellar absorption). The SN-based distance modulus is
larger by about +0.7 mag than the previous Tully-Fisher estimates. However,
possible systematic errors due to ambiguities in the reddening determination
and estimates of the maximum luminosity of SN 2000E may plague the present
distance measurement.Comment: 9 p., 5 figs, accepted for publication in A&A. A reference correcte
Improved distance determination to M51 from supernovae 2011dh and 2005cs
The appearance of two recent supernovae, SN 2011dh and 2005cs, both in M51,
provides an opportunity to derive an improved distance to their host galaxy by
combining the observations of both SNe. We apply the Expanding Photosphere
Method to get the distance to M51 by fitting the data of these two SNe
simultaneously. In order to correct for the effect of flux dilution, we use
correction factors (zeta) appropriate for standard type II-P SNe atmospheres
for 2005cs, but find zeta ~ 1 for the type IIb SN 2011dh, which may be due to
the reduced H-content of its ejecta. The EPM analysis resulted in D_M51 = 8.4
+/- 0.7 Mpc. Based on this improved distance, we also re-analyze the HST
observations of the proposed progenitor of SN 2011dh. We confirm that the
object detected on the pre-explosion HST-images is unlikely to be a compact
stellar cluster. In addition, its derived radius (~ 277$ R_sun) is too large
for being the real (exploded) progenitor of SN 2011dh. The supernova-based
distance, D = 8.4 Mpc, is in good agreement with other recent distance
estimates to M51.Comment: 6 pages, 5 figures, accepted for publication in A&
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