Astron.Astrophys. 427 (2004) 245-250 We have imaged two bona-fide brown dwarfs with TReCS/GEMINI-S and find
mid-infrared excess emission that can be explained by optically thick dust disk
models. In ...the case of the young ($\approx$2Myr) Cha H$\alpha$1 we measure
fluxes at 10.4$\mu$m and 12.3$\mu$m that are fully consistent with a standard
flared disk model and prominent silicate emission. For the $\approx$ 10Myr old
brown dwarf 2MASS1207-3932 located in the TW Hydrae association we find excess
emission at 8.7$\mu$m and 10.4$\mu$m with respect to its photosphere, and
confirm disk accretion as likely cause of its strong activity. Disks around
brown dwarfs likely last at least as long as their low-mass stellar
counterparts in the T-Tauri phase. Grain growth, dust settling, and evolution
of the geometry of brown dwarfs disks may appear on a timescale of 10Myr and
can be witnessed by observations in the mid-infrared.
We report the results of mid-IR observations with VISIR at the VLT of 10 ultracool dwarfs members of the nearby Upper Scorpius OB association in four filters ranging between 8.59 (PAH1) to 12.8 ...\(\mu\)m (Ne II), and one brown dwarf with Spitzer between 3.6 and 24 \(\mu\)m. Seven of our targets are detected in at least one of the bands, and we derive upper limits on the fluxes of the remaining 4. These results combined with previous studies from the literature lead to an improved disk frequency of 50\(\pm\)12%. This frequency is significantly higher than that of accretors (16.3%\(\pm\)6.2%). Only one object showing mid-IR excess also has H\(\alpha\) emission at a level indicating that it must be accreting. Four of the detected targets are multiple system candidates. The observed disk frequency for sub-stellar objects in the Upper Scorpius association is similar to that of stars, consistent with a common formation scenario. It is also similar to the disk fractions observed in younger clusters, suggesting that the disk lifetimes might be longer for ultracool dwarfs than for higher-mass stars.
In the SACY (Search for Associations Containing Young-stars) project we try
to identify associations of stars younger than the Local Association among
HIPPARCOS and/or TYCHO-2 stars later than G0 ...which are counterparts of the
ROSAT X-ray bright sources. High-resolution spectra for the possible optical
counterparts were obtained in order to assess both the youth and the spatial
motion of each target. More than 1000 ROSAT sources were observed, covering a
large area in the Southern Hemisphere. Associations are characterized mainly by
the similarity in UVW velocity space of their proposed member, but other
parameters, as evolutionary age, Li abundance and distribution in space must
also be taken into account. We proposed a method to identify associations when
proper motions and radial velocities are available, but no parallaxes. Using
the method we found eleven associations in the SACY data.
The scientific goal of the SACY (Search for Associations Containing
Young-stars) was to identify possible associations of stars younger than the
Pleiades Association among optical counterparts of the ...ROSAT X-ray bright
sources. High-resolution spectra for possible optical counterparts later than
G0 belonging to HIPPARCOS and/or TYCHO-2 catalogs were obtained in order to
assess both the youth and the spatial motion of each target. More than 1000
ROSAT sources were observed, covering a large area in the Southern Hemisphere.
The newly identified young stars present a patchy distribution in UVW and XYZ,
revealing the existence of huge nearby young associations. Here we present the
associations identified in this survey.
We have imaged two bona-fide brown dwarfs with TReCS/GEMINI-S and find mid-infrared excess emission that can be explained by optically thick dust disk models. In the case of the young ...(\(\approx\)2Myr) Cha H\(\alpha\)1 we measure fluxes at 10.4\(\mu\)m and 12.3\(\mu\)m that are fully consistent with a standard flared disk model and prominent silicate emission. For the \(\approx\) 10Myr old brown dwarf 2MASS1207-3932 located in the TW Hydrae association we find excess emission at 8.7\(\mu\)m and 10.4\(\mu\)m with respect to its photosphere, and confirm disk accretion as likely cause of its strong activity. Disks around brown dwarfs likely last at least as long as their low-mass stellar counterparts in the T-Tauri phase. Grain growth, dust settling, and evolution of the geometry of brown dwarfs disks may appear on a timescale of 10Myr and can be witnessed by observations in the mid-infrared.
In the SACY (Search for Associations Containing Young-stars) project we try to identify associations of stars younger than the Local Association among HIPPARCOS and/or TYCHO-2 stars later than G0 ...which are counterparts of the ROSAT X-ray bright sources. High-resolution spectra for the possible optical counterparts were obtained in order to assess both the youth and the spatial motion of each target. More than 1000 ROSAT sources were observed, covering a large area in the Southern Hemisphere. Associations are characterized mainly by the similarity in UVW velocity space of their proposed member, but other parameters, as evolutionary age, Li abundance and distribution in space must also be taken into account. We proposed a method to identify associations when proper motions and radial velocities are available, but no parallaxes. Using the method we found eleven associations in the SACY data.
The scientific goal of the SACY (Search for Associations Containing Young-stars) was to identify possible associations of stars younger than the Pleiades Association among optical counterparts of the ...ROSAT X-ray bright sources. High-resolution spectra for possible optical counterparts later than G0 belonging to HIPPARCOS and/or TYCHO-2 catalogs were obtained in order to assess both the youth and the spatial motion of each target. More than 1000 ROSAT sources were observed, covering a large area in the Southern Hemisphere. The newly identified young stars present a patchy distribution in UVW and XYZ, revealing the existence of huge nearby young associations. Here we present the associations identified in this survey.
We present the ROSAT All-Sky Survey data in a 126 deg^2 area in and around
the CrA star forming region. With low-resolution spectroscopy of unidentified
ROSAT sources we could find 19 new pre-main ...sequence stars, two of which are
classical T Tauri stars, the others being weak-lined. The spectral types of
these new T Tauri stars range from F7 to M6. The two new classical T Tauri
stars are located towards two small cloud-lets outside of the main CrA cloud.
They appear to be ~10 Myrs old, by comparing their location in the H-R diagram
with isochrones for an assumed distance of 130 pc, the distance of the main CrA
dark cloud. The new off-cloud weak-line T Tauri stars may have formed in
similar cloud-lets, which have dispersed recently. High-resolution spectra of
our new T Tauri stars show that they have significantly more lithium absorption
than zero-age main-sequence stars of the same spectral type, so that they are
indeed young. From those spectra we also obtained rotational and radial
velocities. For some stars we found the proper motion in published catalogs.
The direction and velocity of the 3D space motion - south relative to the
galatic plane - of the CrA T Tauri stars is consistent with the dark cloud
being formed originally by a high-velocity cloud impact onto the galactic
plane, which triggered the star formation in CrA. We also present VRIJHK
photometry for most of the new T Tauri stars to derive their luminosities,
ages, and masses.
We present the ROSAT All-Sky Survey data in a 126 deg^2 area in and around the CrA star forming region. With low-resolution spectroscopy of unidentified ROSAT sources we could find 19 new pre-main ...sequence stars, two of which are classical T Tauri stars, the others being weak-lined. The spectral types of these new T Tauri stars range from F7 to M6. The two new classical T Tauri stars are located towards two small cloud-lets outside of the main CrA cloud. They appear to be ~10 Myrs old, by comparing their location in the H-R diagram with isochrones for an assumed distance of 130 pc, the distance of the main CrA dark cloud. The new off-cloud weak-line T Tauri stars may have formed in similar cloud-lets, which have dispersed recently. High-resolution spectra of our new T Tauri stars show that they have significantly more lithium absorption than zero-age main-sequence stars of the same spectral type, so that they are indeed young. From those spectra we also obtained rotational and radial velocities. For some stars we found the proper motion in published catalogs. The direction and velocity of the 3D space motion - south relative to the galatic plane - of the CrA T Tauri stars is consistent with the dark cloud being formed originally by a high-velocity cloud impact onto the galactic plane, which triggered the star formation in CrA. We also present VRIJHK photometry for most of the new T Tauri stars to derive their luminosities, ages, and masses.
Objectives
To evaluate the potential role of dual energy CT (DECT) to visualize antiangiogenic treatment effects in patients with metastatic renal cell cancer (mRCC) while treated with ...tyrosine-kinase inhibitors (TKI).
Methods
26 patients with mRCC underwent baseline and follow-up single-phase abdominal contrast enhanced DECT scans. Scans were performed immediately before and 10 weeks after start of treatment with TKI. Virtual non-enhanced (VNE) and colour coded iodine images were generated. 44 metastases were measured at the two time points. Hounsfield unit (HU) values for VNE and iodine density (ID) as well as iodine content (IC) in mg/ml of tissue were derived. These values were compared to the venous phase DECT density (CTD) of the lesions. Values before and after treatment were compared using a paired Student’s
t
test.
Results
Between baseline and follow up, mean CTD and DECT-derived ID both showed a significant reduction (p < 0.005). The relative reduction measured in percent was significantly greater for ID than for CTD (49.8 ± 36,3 % vs. 29.5 ± 20.8 %, p < 0.005). IC was also significantly reduced under antiangiogenic treatment (p < 0.0001).
Conclusions
Dual energy CT-based quantification of iodine content of mRCC metastases allows for significantly more sensitive and reproducible detection of antiangiogenic treatment effects.
Key Points
•
A sign of tumour response to antiangiogenic treatment is reduced tumour perfusion
.
•
DECT allows visualizing iodine uptake, which serves as a marker for vascularization
.
•
More sensitive detection of antiangiogenic treatment effects in mRCC is possible
.
