Issue |
A&A
Volume 517, July 2010
|
|
---|---|---|
Article Number | L3 | |
Number of page(s) | 5 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361/201014776 | |
Published online | 30 July 2010 |
The 2008 outburst in the young stellar system Z CMa![[*]](/icons/foot_motif.png)
I. Evidence of an enhanced bipolar wind on the AU-scale
M. Benisty1 - F. Malbet2 - C. Dougados2 - A. Natta1 - J. B. Le Bouquin2 - F. Massi1 - M. Bonnefoy2 - J. Bouvier2 - G. Chauvin2 - O. Chesneau3 - P. J. V. Garcia2,4 - K. Grankin5 - A. Isella6 - T. Ratzka7 - E. Tatulli2 - L. Testi8 - G. Weigelt9 - E. T. Whelan2
1 - INAF-Osservatorio Astrofisico di Arcetri, Largo
E. Fermi 5, 50125 Firenze, Italy
2 -
Laboratoire d'Astrophysique de Grenoble, CNRS-UJF UMR 5571,
414 rue de la Piscine, 38400 Saint Martin d'Hères, France
3 -
Laboratoire A. H. Fizeau, UMR 6525, Université de Nice-Sophia
Antipolis, Parc Valrose, 06108 Nice Cedex 02, France
4 -
Universidade do Porto, Faculdade de Engenharia, SIM Unidade
FCT 4006, Rua Dr. Roberto Frias, s/n 4200-465 Porto, Portugal
5 -
Crimean Astrophysical Observatory, 98409 Nauchny, Crimea,
Ukraine
6 -
Caltech, MC 249-17, 1200 East California Blvd, Pasadena, CA 91125, USA
7 -
Universitäts-Sternwarte München Scheinerstr. 1, 81679 München, Germany
8 -
European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748
Garching, Germany
9 -
Max Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121
Bonn, Germany
Received 12 April 2010 / Accepted 26 June 2010
Abstract
Context. Accretion is a fundamental process in star
formation. Although the time evolution of accretion remains a matter of
debate, observations and modelling studies suggest that episodic
outbursts of strong accretion may dominate the formation of the central
protostar. Observing young stellar objects during these elevated
accretion states is crucial to understanding the origin of unsteady
accretion.
Aims. Z CMa is a pre-main-sequence binary system
composed of an embedded Herbig Be star, undergoing photometric
outbursts, and a FU Orionis star. This system therefore provides a
unique opportunity to study unsteady accretion processes. The Herbig Be
component recently underwent its largest optical photometric outburst
detected so far. We aim to constrain the origin of this outburst by
studying the emission region of the HI Br line, a powerful tracer of accretion/ejection processes on the AU-scale in young stars.
Methods. Using the AMBER/VLTI instrument at spectral resolutions
of 1500 and 12 000, we performed spatially and spectrally resolved
interferometric observations of the hot gas emitting across the Br emission
line, during and after the outburst. From the visibilities and
differential phases, we derive characteristic sizes for the Br
emission and spectro-astrometric measurements across the line, with respect to the continuum.
Results. We find that the line profile, the astrometric signal,
and the visibilities are inconsistent with the signature of either a
Keplerian disk or infall of matter. They are, instead, evidence of a
bipolar wind, maybe partly seen through a disk hole inside the dust
sublimation radius. The disappearance of the Br emission
line after the outburst suggests that the outburst is related to a
period of strong mass loss rather than a change of the extinction along
the line of sight.
Conclusions. Apart from the photometric increase of the system,
the main consequence of the outburst is to trigger a massive bipolar
outflow from the Herbig Be component. Based on these conclusions,
we speculate that the origin of the outburst is an event of enhanced
mass accretion, similar to those occuring in EX Ors and
FU Ors.
Key words: circumstellar matter - stars: variables: T Tauri - herbig Ae/Be - stars: winds - outflows - methods: obsevational - stars: individual: Z CMa - techniques: interferometric
1 Introduction
Accretion plays an important role in star and planet formation. For many years, it was considered to be a slow quasi-stationary process (e.g., Stahler 1988), occurring mostly through a viscous disk ending in its inner part by a boundary layer with the star (e.g., Bertout et al. 1988) or by magnetospheric funnels (e.g., Calvet & Hartmann 1992; Koenigl 1991). However, this scenario has been challenged by observations (e.g., Kenyon et al. 1990; Evans et al. 2009) that suggest that the accretion process could be time-variable and occur quickly by means of short high mass accretion rate bursts. Studying the very inner region of a young stellar object that is known to experience episodic photometric outbursts is thus of prime importance to understand the role of accretion in the formation of the star and its environment.Z CMa is a pre-main-sequence binary with a separation of 0.1
(Barth et al. 1994; Koresko et al. 1991) located at a distance estimated from 930 to 1150 pc
(e.g., Kaltcheva & Hilditch 2000; Clariá 1974). The primary, embedded in a dust
cocoon, was identified as a Herbig Be star based on
spectropolarimetry (Whitney et al. 1993). It is surrounded by
an inclined disk, possibly a circumbinary disk, as inferred from millimeter observations
(Alonso-Albi et al. 2009),
and dominates the infrared continuum and total
luminosity of the system. In contrast, the secondary is the major
source of continuum emission at visual wavelengths. Although the
secondary has not undergone a large outburst
this century, it was identified as a FU Or object based on its
broad
double-peaked optical absorption lines, which are typical of a
circumstellar disk that
undergoes a strong accretion, and spectral type of
F-G (Hartmann et al. 1989). In the past twenty years, the Z CMa
system exhibited repeated brightness variations, of
0.5-1
visual magnitude, which were attributed to the Herbig Be star
(e.g., van den Ancker et al. 2004).
Z CMa is clearly associated with
a bipolar outflow that extends to 3.6 pc along
PA
240
(Evans et al. 1994; Poetzel et al. 1989). Garcia et al. (1999) detected a
micro-jet in the [OI] 6300 Å line in the same direction, and concluded
that the optical emission-line spectrum and the jet are associated with the
primary.
However, the innermost environments of the Z CMa components have been
poorly studied. Two broad-band interferometric measurements
have been obtained, allowing only characteristic sizes of the
K-band continuum emission to be
derived (Millan-Gabet et al. 2006; Monnier et al. 2005).
In January 2008, Z CMa's brightness increased by about two visual magnitudes (Grankin & Artemenko 2009), representing the largest outburst observed in the past 90 years. Based on spectropolarimetric observations, Szeifert et al. (2010) concluded that this outburst is associated with the Herbig Be star.
The study presented in this paper is part of a large observational
campaign targeting Z CMa during this outburst that aims to understand
its origin (Bonnefoy et al., in prep.; Bouvier et al., in prep.; Ratzka
et al., in prep.; Whelan et al., in prep.). The
overall spectral energy distribution of the system is strongly
modified during the outburst at wavelengths shorter than 10 m
(Bonnefoy et al., in prep.; Ratzka et al., in prep.), which indicates
that the outburst originates close to the star. To directly probe the
morphology of the hot gas in the inner AUs, we took
advantage of the spatial and spectral resolution available at the VLTI
to perform
-arcsecond spectro-astrometry. We resolved the K-band
emission of the hot gas surrounding each star at the milliarcsecond
resolution. This paper reports the first spatially and
spectrally resolved observations in Br
of a young star. We
also observed the binary system after the outburst. In
Sect. 2, we present the observations and the data processing. In
Sects. 3 and 4, we describe and discuss the results.
2 Observations and data processing
Z CMa was observed at the Very Large Telescope Interferometer (VLTI; Schöller 2007), using the AMBER instrument that allows the simultaneous combination of three beams in the near-infrared (Petrov et al. 2007). The instrument delivers spectrally dispersed interferometric observables (visibilities, closure phases, differential phases) at spectral resolutions up to 12 000.In the following, we present K-band observations taken in the medium spectral
resolution mode (MR;
)
with the 8.2 m Unit Telescopes (UTs)
as well as with the 1.8 m Auxiliary Telescopes (ATs), and in
the high spectral resolution mode (HR;
)
with the ATs. The data were obtained within programs of guaranteed
time, Director's
Discretionary Time, and Open Time observations. Z CMa was
observed with 11 different baselines of 4 VLTI
configurations, during 5 nights in December 2008 and one night in
January 2010. The longest baseline is
120 m corresponding to a
maximum angular resolution of 3.7 mas. A summary
of the observations presented in this paper is given in Table 1.
With the UTs, the observations are coupled with the use of adaptive
optics and the resulting field of view ranges from 50 to
60 mas. This allowed us to spatially resolve the binary and obtain
separate measurements of the FU Or and the Herbig Be. In
contrast, the ATs field-of-view, ranging from 230 to 280 mas, includes
both stars and the interferometric signal results from both emissions. In
addition to Z CMa, calibrators (HD 45420, HD 60742, HD 55137, HD 55832) were observed to correct for
instrumental
effects. All observations were performed using the
fringe-tracker FINITO (Le Bouquin et al. 2008).
The data reduction was performed following standard procedures
described in Tatulli et al. (2007) and Chelli et al. (2009), using the amdlib package,
release 2.99, and the yorick interface provided by the
Jean-Marie Mariotti
Center.
Raw spectral visibilities, differential phases, and closure phases were extracted for
all the frames of each observing file. A selection of 80% of the
highest quality frames was made and
consecutive observations were merged to enhance
the signal-to-noise ratio.
The accuracy of the wavelength/velocity calibration is
50 km s-1.
Because the K-band continuum measured by the ATs (due to both
stars) is very resolved on long baselines (
), the
observations obtained on the G1-A0 and K0-A0 baselines could not be
exploited. The absolute value
of the visibilities obtained with the UT baselines could not be
determined due to random vibrations of the telescopes. However, this
issue affects all spectral channels in the same way, and does not
modify our conclusions.
Table 1: Log of the observations. R is the spectral resolution.
![]() |
Figure 1:
Interferometric measurements of the Z CMa
binary system in December 2008. The binary system is
sketched at the bottom left. Left panels:
MR spectrum, squared visibilities (normalized to the continuum
ones,
|
Open with DEXTER |
3 Results
We recall that the visibilities provide information about the spatial extent of the emission, and decrease as the extension increases. Differential phases provide a measurement of the photocenter displacements across the sky, projected along the baseline direction. They can therefore be converted into differential spectro-astrometric shifts. They are measured relative to the continuum, for which we assume a zero phase. Finally, the closure phases are related to the asymmetry of the brightness distribution (e.g., they are null for a point-symmetric object).We show in Figs. 1 and 2 a subsample of
the observations that illustrate the main characteristics of the data. Since the absolute
values of the visibilities measured with the UTs are unknown, we
normalized the continuum values to 1 - even though the emission
is resolved. The left and middle columns of Fig. 1 present
examples of the MR observations obtained with the UTs for each star
during the outburst. Each column includes a spectrum (normalized to
the continuum), squared visibilities, differential phases, and closure phases. For
the FU Or (left panels), within the error bars, the spectrum
shows Br in neither emission nor absorption. Consequently, no change
in the visibilities or phases across the line is expected/seen.
In contrast, the Herbig Be star exhibits a clear Br
line in
emission (middle panels), although at this spectral resolution
(
km s-1), the line is not spectrally resolved. The
visibility increases through the line and the
differential phases produce an S-shape variation. The closure phases
differ from zero, with values of 25
.
The phase, line, and visibility signals are present
from
-600 to 500 km s-1, although because of the low line-to-continuum
ratio in the extended wings, the flux and visibilities appear narrower.
Within the large errors, no variation in the closure phases is
detected across the line.
The right part of the figure shows measurements
obtained with the ATs,
i.e., with both stars in the field of view. In this case, the level of
continuum is determined by both stellar components.
These panels present observations obtained in HR.
In this case, the line is spatially and spectrally resolved (
km s-1), and the spectra exhibit a
clear double-peaked and asymmetric profiles, with less emission at
blueshifted velocities. The spectral visibilities present a similar profile.
Finally, Fig. 2 compares the spectra and the visibilities obtained during and after the outburst: the emission line, and the signature in the visibilities, disappear after the outburst. Plotted within a large velocity range, the visibilities show a typical signature of binarity (i.e., a cosine modulation), in agreement with the system main characteristics (separation, position angle, flux ratio; Bonnefoy et al., in prep.).
From the visibilities, one can locate the emission at
each velocity and distinguish between various scenarios capable of
producing the line. The visibility increase within
the line implies that the Br emitting region is more compact
than the one responsible for the continuum. To derive the characteristic sizes
of the region emitting Br
only, for each spectral channel of the
HR measurements, one
has to substract the underlying continuum to first determine the
visibility of the line only (Weigelt et al. 2007). These estimates can
only be performed using the data gathered with the ATs, for which reliable absolute values for the Br
visibilities are obtained. Using a model of an uniform ring,
the emission in the line has a typical extension (ring diameter) of
1.6 mas at zero
velocity, and
2.5 mas at higher velocities (
100 km s-1),
i.e., from
1.5 to
2.6 AU,
depending on the distance. As the continuum emission measured with the ATs
includes both stars, it is not direct to establish
the typical size of the Herbig Be continuum. In contrast, the UTs data
include only one stellar component. Although no
absolute visibility values can be obtained, size ratios between the
line and the continuum can be derived. Using the sizes
previously estimated for the line from the ATs data, typical sizes of
3.4 mas (
3.6 AU) for the Herbig Be K-band continuum can
be determined, in agreement with the previous estimate (
3.9 mas
in 2004; Monnier et al. 2005). Considering a dust sublimation temperature
around 1500-2000 K (Pollack et al. 1994), and the stellar properties
determined by van den Ancker et al. (2004), the inner edge of the dusty disk must be
located at
4-7 AU, in agreement with our findings. An asymmetry
in the inclined inner disk could explain the non-zero closure phases
measured at a level similar to other
Herbig AeBe stars (Kraus et al. 2009; Benisty et al. 2010).
![]() |
Figure 2:
MR normalized spectra and visibilities during (2008)
and after the outburst (2010). The slopes of the visibility curves depend on the binary
characteristics and on the observing set up, that differs in the two
observations. Note the disappearance of the Br |
Open with DEXTER |
The differential phases
can be expressed in terms of
photocenter displacements p (in arcseconds), following
Lachaume (2003), given by
,
where
and B are the wavelength and the projected
baseline length of the
observations, respectively. p is the projection along the baseline
direction, of the 2D photocenter vector
in the plane of the sky
(i.e., of a spectro-astrometric signal). We fitted all the differential phases along the
6 available baselines
with a single vector
,
independently of each spectral
channel. The results are presented in Fig. 3. The left
panels show the differential phases and the best solution
for
.
The middle plot gives
in a 2D map of the plane of the
sky. Clear asymmetric displacements, up to
150
-arcseconds, are observed, both at red-shifted
and blue-shifted velocities.
In this case,
accounts for the emission of
both the line and the continuum. Substracting the continuum
contribution to determine the photocenter displacements,
,
due to the line only, is difficult, as it
has to be done in the complex visibility plane. We
provide such an attempt in the velocity range where the line is
clearly detected ([-350; 350] km s-1, with line-to-continuum ratio larger
than 1.05). As can be seen in Fig. 3, right, the
displacements are much larger (up to
1 mas) with the largest
measured at the highest velocities, and appear more
spread. Nonetheless, the observed asymmetry is
still consistent with the closure phase measurements that show no
change through the line, within the large errors.
4 Evidence of a bipolar wind
As has already been discussed in previous studies (Eisner et al. 2009; Kraus et al. 2008), the Br line could be emitted by a variety of
mechanisms, such as accretion of matter onto the star, in
a gaseous disk, or in outflowing matter. The spectra obtained at
high spectral resolution show a double-peaked
and asymmetric profile that can be interpreted in the context of the
formation of optically thick lines in a dense environment with a
temperature gradient (Cesaroni 1995; Kurosawa et al. 2006).
Formation of the Br line in an
infalling envelope of gas can be ruled out. Considering that the line
excitation temperature increases towards the star, if the line is
emitted in infall of matter, or accretion flows, the profile would be
double peaked but with an opposite asymmetry to what is observed
(Fig. 1, right; i.e., with a lower emission at redshifted velocities;
see Walker et al. 1994; Hartmann et al. 1994). In addition, in that case, the smallest
extension and photocenter displacements would be expected at the
highest velocities, which is in disagreement with our findings (see
Figs. 1 and 3).
The possibility that the Br line forms in the hot layers of the
gaseous disk can also be ruled out. If one considers that the
circumstellar disk surrounding the Herbig Be
star is perpendicular to the large-scale jet at PA
240
,
it would be
expected that the velocities projected onto the line of sight cancel
out along the semi-minor axis, while large spectro-astrometric
displacements are seen along this axis at high velocities
(Fig. 3). Apart from this, the displacements increase with
velocity while Keplerian rotation should behave in the opposite way,
and a phase signal is measured up to high
velocities (
500 km s-1), which are much larger than the expected Keplerian
velocities (
100-120 km s-1 at
1 AU). It therefore seems
unlikely that the Br
line is emitted in the disk.
![]() |
Figure 3:
Left: differential phases measured with the
UTs (black crosses and lines). The dots in different colors
represent various velocity channels, from dark blue (for
|
Open with DEXTER |
We consider that the most likely origin of the Br emission
is a wind. Strong winds are expected to take place in massive
Herbig Be (Malbet et al. 2007; Nisini et al. 1995), and could be responsible for the
Br
emission. The double peaked and asymmetric line profile is
consistent with outflowing matter emitting in optically thick
lines (Hartmann et al. 1990). The visibilities and the 2D maps of the
astrometric signal also support this
conclusion as the blue- and redshifted emissions are located on each
side of the possible disk position angle, with the largest Br
displacements and
characteristic sizes being derived at higher velocities. Our
observations suggest that the disk is slightly inclined, to
allow both red- and blueshifted
emissions to be seen. We may be
seeing the emission from a wind partly through an optically thin
inner hole in the optically thick dusty disk (Whelan et al. 2004; Takami et al. 2001). Alternatively, if the inner gaseous disk were optically thick, we
may be seeing the redshifted emission through a much smaller hole and via
scattering on the disk surface. Whether the innermost disk is
optically thick or not cannot be determined with our observations
and no reliable estimate of the mass accretion rate exists for such
high mass young stars. However, the presence of the CO overtone
lines in emission (Bonnefoy et al., in prep.) is indicative of a much lower
mass accretion rate
than those derived for FU Ors
(
10-5
yr-1; Carr 1989; Calvet et al. 1991). At the spatial resolutions provided by the VLTI, we
trace the regions close to the inner disk hole and it is therefore unsurprising that
we could detect redshifted emission, while on scales of 10-100 AU,
the redshifted lobe is obscured by the circumstellar disk
(Garcia et al. 1999; Poetzel et al. 1989; Whelan et al., in
prep.). During this outburst, deep
blueshifted absorption was detected
in the Balmer lines from zero velocity to
700 km s-1, in
addition to the absence of redshifted emission at similar velocities
(Szeifert et al. 2010; Bouvier et al., in prep.),
supporting our conclusion that there is a strong wind in the
Herbig Be.
Could our new observations be tracing the inner parts of the parsec scale outflow? As shown in Fig. 3, the astrometric signal is detected at a slightly different position angle and at these spatial scales, it is unlikely that the jet is already collimated. Our observations exclude a fully spherical wind since in that case no displacement would be expected between the redshifted and blueshifted emission lobes. The derived spectro-astrometric signatures favor a bipolar wind, maybe unrelated to the jet, but can not determine whether its geometry is that of a disk-wind or a stellar wind.
After detecting the same level of optical polarisation in both
continuum and spectral lines along a position angle roughly
perpendicular to the large-scale jet, Szeifert et al. (2010) concluded that
this outburst is related to a change in the path along which the photons
escape from the dust cocoon.
The disappearance of the Br emission line, with respect to the
continuum, after the outburst, suggests that its emission is related to
the outburst. A strong mass ejection event could account for
the deep blueshifted absorption features seen in the Balmer lines that
are emitted close to the star as well as for the
Br
line emitted in outer layers of the wind. Outside the
outburst, the wind disappears or is more likely to be maintained at a much
smaller mass loss rate. Based on these
conclusions, one can speculate about the origin of the outburst, as
being driven by an event of enhanced mass accretion, similar to the EX Ors
and FU Ors outbursts (Zhu et al. 2010). In that case, this would
suggest a strong link between mass accretion and ejection during the
outburst, probably coupled with a magnetic field as in lower-mass
young stars.
5 Conclusions
We have presented spatially and spectrally resolved interferometric observations of the K-band emission in the Z CMa system. These observations were performed during the largest photometric outburst detected so far, that occurred in the innermost regions of the Herbig Be star.We found that the Br line profile, the astrometric signal, and the
characteristic sizes across the line are inconsistent with a
Keplerian disk or with infall of matter. They are, instead, evidence
of a bipolar wind seen through a disk hole, inside the
dust sublimation radius. The disappearance of the Br
emission
line after the outburst suggests that the outburst is related to a
period of strong mass loss. Based on these conclusions, we have
speculated that the origin of the outburst is an event of enhanced
mass accretion, and that it does not result from a change in the system
obscuration by dust. If this were valid, our results would suggest that
the link between
mass accretion and ejection as observed for quiescent T Tauri stars
can also be at play in more massive young stars, and in high-accretion
states.
Finally, this paper illustrates the great potential of the combination
of spectro-astrometric and interferometric techniques for observing
structures on -arcsecond scales.
We thank the VLTI team at Paranal, as well as R. Cesaroni, S. Antoniucci, L. Podio, P. Stee and M. van den Ancker for fruitful discussions. We thank the anonymous referee for helpful comments. M.B. acknowledges funding from INAF (grant ASI-INAF I/016/07/0).
References
- Alonso-Albi, T., Fuente, A., Bachiller, R., et al. 2009, A&A, 497, 117 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Barth, W., Weigelt, G., & Zinnecker, H. 1994, A&A, 291, 500 [NASA ADS] [Google Scholar]
- Benisty, M., Natta, A., Isella, A., et al. 2010, A&A, 511, A74 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Bertout, C., Basri, G., & Bouvier, J. 1988, ApJ, 330, 350 [NASA ADS] [CrossRef] [Google Scholar]
- Calvet, N., & Hartmann, L. 1992, ApJ, 386, 239 [NASA ADS] [CrossRef] [Google Scholar]
- Calvet, N., Patino, A., Magris, G. C., & D'Alessio, P. 1991, ApJ, 380, 617 [NASA ADS] [CrossRef] [Google Scholar]
- Carr, J. S. 1989, ApJ, 345, 522 [NASA ADS] [CrossRef] [Google Scholar]
- Cesaroni, R. 1995, A&AS, 114, 397 [NASA ADS] [Google Scholar]
- Chelli, A., Utrera, O. H., & Duvert, G. 2009, A&A, 502, 705 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Clariá, J. J. 1974, A&A, 37, 229 [NASA ADS] [Google Scholar]
- Eisner, J. A., Graham, J. R., Akeson, R. L., & Najita, J. 2009, ApJ, 692, 309 [NASA ADS] [CrossRef] [Google Scholar]
- Evans, N., Balkum, S., Levreault, R., et al. 1994, ApJ, 424, 793 [NASA ADS] [CrossRef] [Google Scholar]
- Evans, N. J., Dunham, M. M., Jørgensen, J. K., et al. 2009, ApJS, 181, 321 [NASA ADS] [CrossRef] [Google Scholar]
- Garcia, P. J. V., Thiébaut, E., & Bacon, R. 1999, A&A, 346, 892 [NASA ADS] [Google Scholar]
- Grankin, K. N., & Artemenko, S. A. 2009, IBVS, 5905, 1 [Google Scholar]
- Hartmann, L., Avrett, E. H., Loeser, R., & Calvet, N. 1990, ApJ, 349, 168 [NASA ADS] [CrossRef] [Google Scholar]
- Hartmann, L., Hewett, R., & Calvet, N. 1994, ApJ, 426, 669 [NASA ADS] [CrossRef] [Google Scholar]
- Hartmann, L., Kenyon, S. J., Hewett, R., et al. 1989, ApJ, 338, 1001 [NASA ADS] [CrossRef] [Google Scholar]
- Kaltcheva, N. T., & Hilditch, R. W. 2000, MNRAS, 312, 753 [NASA ADS] [CrossRef] [Google Scholar]
- Kenyon, S. J., Hartmann, L. W., Strom, K. M., & Strom, S. E. 1990, AJ, 99, 869 [NASA ADS] [CrossRef] [Google Scholar]
- Koenigl, A. 1991, ApJ, 370, L39 [NASA ADS] [CrossRef] [Google Scholar]
- Koresko, C. D., Beckwith, S. V. W., Ghez, A. M., et al. 1991, AJ, 102, 2073 [NASA ADS] [CrossRef] [Google Scholar]
- Kraus, S., Hofmann, K., Benisty, M., et al. 2008, A&A, 489, 1157 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Kraus, S., Hofmann, K., Malbet, F., et al. 2009, A&A, 508, 787 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Kurosawa, R., Harries, T. J., & Symington, N. H. 2006, MNRAS, 370, 580 [NASA ADS] [CrossRef] [Google Scholar]
- Lachaume, R. 2003, A&A, 400, 795 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Le Bouquin, J.-B., Bauvir, B., Haguenauer, P., et al. 2008, A&A, 481, 553 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Malbet, F., Benisty, M., de Wit, W., et al. 2007, A&A, 464, 43 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Millan-Gabet, R., Monnier, J. D., Akeson, R. L., et al. 2006, ApJ, 641, 547 [NASA ADS] [CrossRef] [Google Scholar]
- Monnier, J. D., Millan-Gabet, R., Billmeier, R., et al. 2005, ApJ, 624, 832 [NASA ADS] [CrossRef] [Google Scholar]
- Nisini, B., Milillo, A., Saraceno, P., & Vitali, F. 1995, A&A, 302, 169 [NASA ADS] [Google Scholar]
- Petrov, R. G., Malbet, F., Weigelt, G., et al. 2007, A&A, 464, 1 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Poetzel, R., Mundt, R., & Ray, T. P. 1989, A&A, 224, L13 [NASA ADS] [Google Scholar]
- Pollack, J. B., Hollenbach, D., Beckwith, S., et al. 1994, ApJ, 421, 615 [NASA ADS] [CrossRef] [Google Scholar]
- Schöller, M. 2007, New Astron. Rev., 51, 628 [NASA ADS] [CrossRef] [Google Scholar]
- Stahler, S. W. 1988, ApJ, 332, 804 [NASA ADS] [CrossRef] [Google Scholar]
- Szeifert, T., Hubrig, S., Schöller, M., et al. 2010, A&A, 509, L7 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Takami, M., Bailey, J., Gledhill, T. M., et al. 2001, MNRAS, 323, 177 [NASA ADS] [CrossRef] [Google Scholar]
- Tatulli, E., Millour, F., Chelli, A., et al. 2007, A&A, 464, 29 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- van den Ancker, M., Blondel, P., Tjin A Djie, H., et al. 2004, MNRAS, 349, 1516 [NASA ADS] [CrossRef] [Google Scholar]
- Walker, C. K., Narayanan, G., & Boss, A. P. 1994, ApJ, 431, 767 [NASA ADS] [CrossRef] [Google Scholar]
- Weigelt, G., Kraus, S., Driebe, T., et al. 2007, A&A, 464, 87 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Whelan, E. T., Ray, T. P., & Davis, C. J. 2004, A&A, 417, 247 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Whitney, B., Clayton, G., Schulte-Ladbeck, R., et al. 1993, ApJ, 417, 687 [NASA ADS] [CrossRef] [Google Scholar]
- Zhu, Z., Hartmann, L., Gammie, C. F., et al. 2010, ApJ, 713, 1134 [NASA ADS] [CrossRef] [Google Scholar]
Footnotes
- ... Z CMa
- Based on observations collected at the VLTI (ESO Paranal, Chile) with programs 282.C-5031, 082.C-0376, 084.C-0162.
- ...
Center
- http://www.jmmc.fr
All Tables
Table 1: Log of the observations. R is the spectral resolution.
All Figures
![]() |
Figure 1:
Interferometric measurements of the Z CMa
binary system in December 2008. The binary system is
sketched at the bottom left. Left panels:
MR spectrum, squared visibilities (normalized to the continuum
ones,
|
Open with DEXTER | |
In the text |
![]() |
Figure 2:
MR normalized spectra and visibilities during (2008)
and after the outburst (2010). The slopes of the visibility curves depend on the binary
characteristics and on the observing set up, that differs in the two
observations. Note the disappearance of the Br |
Open with DEXTER | |
In the text |
![]() |
Figure 3:
Left: differential phases measured with the
UTs (black crosses and lines). The dots in different colors
represent various velocity channels, from dark blue (for
|
Open with DEXTER | |
In the text |
Copyright ESO 2010
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