30 research outputs found
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
Dust Emission Features in NGC 7023 between 0.35 and 2.5 micron: Extended Red Emission (0.7 micron) and Two New Emission Features (1.15 and 1.5 micron)
We present 0.35 to 2.5 micron spectra of the south and northwest filaments in
the reflection nebula NGC 7023. These spectra were used to test the theory of
Seahra & Duley that carbon nanoparticles are responsible for Extended Red
Emission (ERE). Our spectra fail to show their predicted second emission band
at 1.0 micron even though both filaments exhibit strong emission in the
familiar 0.7 micron ERE band. The northwest filament spectrum does show one,
and possibly two, new dust emission features in the near-infrared. We clearly
detect a strong emission band at 1.5 micron which we tentatively attribute to
beta-FeSi_2 grains. We tentatively detect a weaker emission band at 1.15 micron
which coincides with the location expected for transitions from the conduction
band to mid-gap defect states of silicon nanoparticles. This is added evidence
that silicon nanoparticles are responsible for ERE as they already can explain
the observed behavior of the main visible ERE band.Comment: 9 pages, color figures, accepted to the ApJ, color and b/w versions
available at http://dirty.as.arizona.edu/~kgordon/papers/ere_1um.htm
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
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
Toward Understanding the B[e] Phenomenon. II. New Galactic FS CMa Stars
FS CMa stars form a group of objects with the B[e] phenomenon that were previously known as unclassified B[e] stars or B[e] stars with warm dust (B[e]WD) until recently. They exhibit strong emission-line spectra and strong IR excesses, most likely due to recently formed circumstellar dust. These properties have been suggested to be due to ongoing or recent rapid mass exchange in binary systems with hot primaries and various types of secondaries. The first paper of this series reported an analysis of the available information about previously known Galactic objects with the B[e] phenomenon, the initial selection of the FS CMa group objects, and a qualitative explanation of their properties. This paper reports the results of our new search for more FS CMa objects in the IRAS Point Source Catalog. We present new photometric criteria for identifying FS CMa stars as well as the first results of our observations of nine new FS CMa group members. With this addition, the FS CMa group has now 40 members, becoming the largest among the dust-forming hot star groups. We also present nine objects with no evidence for the B[e] phenomenon, but with newly discovered spectral line emission and /or strong IR excesses.Fil: Miroshnichenko, A. S.. The University Of North Carolina At Greensboro; Estados UnidosFil: Manset, N.. Canada France Hawaii Telescope; Estados UnidosFil: Kusakin, A.V.. Lomonosov Moscow State University; Rusia. Fesenkov Astrophysical Institute; RusiaFil: Chentsov, E.L.. Russian Academy Of Sciences; RusiaFil: Klochkova, V. G.. Russian Academy Of Sciences; RusiaFil: Zharikov, S. V.. Universidad Nacional Autónoma de México; MéxicoFil: Gray, R. O.. Appalachian State University (appstate);Fil: Grankin, K. N.. Ulugh Beg Astronomical Institute Uzbekistan Academy Of Sciences; UzbekistánFil: Gandet, T. L.. Lizard Hollow Observatory; Estados UnidosFil: Bjorkman, K. S.. University Of Toledo (utoledo); Estados UnidosFil: Rudy, R. J.. The Aerospace Corporation; Estados UnidosFil: Lynch, D. K.. The Aerospace Corporation; Estados UnidosFil: Venturini, C. C.. The Aerospace Corporation; Estados UnidosFil: Mazuk, S.. The Aerospace Corporation; Estados UnidosFil: Puetter, R. C.. University of California at San Diego; Estados UnidosFil: Perry, R. B.. National Aeronautics and Space Administration; Estados UnidosFil: Levato, Orlando Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Grosso, Monica Gladys. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Bernabei, S.. Istituto Nazionale di Astrofisica; ItaliaFil: Polcaro, V. F.. Istituto Nazionale di Astrofisica; ItaliaFil: Viotti, R. F.. Istituto Nazionale di Astrofisica; ItaliaFil: Norci, L.. Dublin City University; IrlandaFil: Kuratov, K. S.. Fesenkov Astrophysical Institute; Kazajistá
B[e] Stars with Warm Dust: Revealing the Nature of Unclassified B[e] Stars and Expanding the Family
Until recently, unclassified B[e] stars represented half of the entire B[e] group. Our study of these objects with strong emission-line spectra and IRAS fluxes, decreasing toward longer wavelengths, resulted in a suggestion that they currently form dust in their envelopes. The objects have been tentatively called B[e] stars with warm dust (B[e]WD). Their luminosity range (?3 orders of magnitude) is much larger compared to previous suggestions that dust formation occurs only near very luminous hot stars. A significant fraction of B[e]WD are recognized or suspected binaries. The group has been expanded with both previously detected hot emission-line stars with IR fluxes, typical for confirmed B[e]WD, and new candidates, found in recent all-sky surveys. Currently the number of B[e]WD members and candidates is ?60 with an opportunity to find more in existing stellar catalogs. Main observational and physical properties of B[e]WD and their envelopes are summarized. Our results on newly found group members are presented. Partially based on observations obtained at the Canada-France-Hawaii Telescope (CFHT).Fil: Miroshnichenko, A. S.. University of North Carolina at Greensboro; Estados UnidosFil: Bernabei, S.. Istituto Nazionale di Astrofisica; ItaliaFil: Bjorkman, K. S.. University Of Toledo (utoledo); Estados UnidosFil: Chentsov, E. L.. Russian Academy of Sciences; RusiaFil: Klochkova, V. G.. Russian Academy of Sciences; RusiaFil: Gray, R. O.. Appalachian State University; Estados UnidosFil: Levato, H.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Grosso, Monica Gladys. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Hinkle, K. H.. National Optical Astronomy Observatory; Estados UnidosFil: Kuratov, K. S.. Fesenkov Astrophysical Institute; KazajistánFil: Kusakin, A. V.. Universitetskij pr; RusiaFil: García Lario, P.. European Space Astronomy Centre; EspañaFil: Perea Calderón, J. V.. European Space Astronomy Centre; EspañaFil: Polcaro, V. F.. Istituto di Astrofisica Spaziale e Fisica Cosmica; ItaliaFil: Viotti, R. F.. Istituto di Astrofisica Spaziale e Fisica Cosmica; ItaliaFil: Norci, L.. Dublin City University; IrlandaFil: Manset, N.. Canada France Hawaii Telescope; Estados UnidosFil: Men’shchikov, A. B.. Saint Mary’s University; CanadáFil: Rudy, R. J.. The Aerospace Corporation; Estados UnidosFil: Lynch, D. K.. The Aerospace Corporation; Estados UnidosFil: Venturini, C. C.. The Aerospace Corporation; Estados UnidosFil: Mazuk, S.. The Aerospace Corporation; Estados UnidosFil: Puetter, R. C.. University of California; Estados UnidosFil: Perry, R. B.. National Aeronautics and Space Administration; Estados UnidosFil: Gandet, T. L.. Lizard Hollow Observatory; Estados Unido
Variability of Disk Emission in Pre-Main Sequence and Related Stars. I. HD 31648 and HD 163296 - Isolated Herbig Ae Stars Driving Herbig-Haro Flows
Infrared photometry and spectroscopy covering a time span of a quarter
century are presented for HD 31648 (MWC 480) and HD 163296 (MWC 275). Both are
isolated Herbig Ae stars that exhibit signs of active accretion, including
driving bipolar flows with embedded Herbig-Haro (HH) objects. HD 163296 was
found to be relatively quiescent photometrically in its inner disk region, with
the exception of a major increase in emitted flux in a broad wavelength region
centered near 3 microns in 2002. In contrast, HD 31648 has exhibited sporadic
changes in the entire 3-13 micron region throughout this span of time. In both
stars the changes in the 1-5 micron flux indicate structural changes in the
region of the disk near the dust sublimation zone, possibly causing its
distance from the star to vary with time. Repeated thermal cycling through this
region will result in the preferential survival of large grains, and an
increase in the degree of crystallinity. The variability observed in these
objects has important consequences for the interpretation of other types of
observations. For example, source variability will compromise models based on
interferometry measurements unless the interferometry observations are
accompanied by nearly-simultaneous photometric data.Comment: 55 pages, 18 figures, 2 tables, Accepted by Ap
A new spectroscopic and interferometric study of the young stellar object V645 Cyg
We present the results of high-resolution optical spectroscopy,
low-resolution near-IR spectroscopy and near-infrared speckle interferometry of
the massive young stellar object candidate V645 Cyg, acquired to refine its
fundamental parameters and the properties of its circumstellar envelope.
Speckle interferometry in the - and -bands and an optical spectrum in the
range 5200--6680 \AA with a spectral resolving power of = 60 000 were
obtained at the 6-m telescope of the Russian Academy of Sciences. Another
optical spectrum in the range 4300--10500 \AA with = 79 000 was obtained at
the 3.6-m CFHT. Low-resolution spectra in the ranges 0.46--1.4 m and
1.4--2.5 m with 800 and 700, respectively, were obtained
at the 3-m Shane telescope of the Lick Observatory. Using a novel kinematical
method based on the non-linear modeling of the neutral hydrogen density profile
in the direction toward the object, we propose a distance of 0.2
kpc. We also suggest a revised estimate of the star's effective temperature,
T25 000 K. We resolved the object in both - and -bands.
We conclude that V645 Cyg is a young, massive, main-sequence star, which
recently emerged from its cocoon and has already experienced its protostellar
accretion stage. The presence of accretion is not necessary to account for the
high observed luminosity of (2--6) M yr. The
receding part of a strong, mostly uniform outflow with a terminal velocity of
800 km s is only blocked from view far from the star, where
forbidden lines form.Comment: 14 pages, 10 figure