| 1. |
|
|
| 2. |
- Wang, Jason J., et al.
(författare)
-
Keck/NIRC2 L'-Band Imaging of Jovian-Mass Accreting Protoplanets around PDS 70
- 2020
-
Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 159:6
-
Tidskriftsartikel (refereegranskat)abstract
- We present L'-band imaging of the PDS 70 planetary system with Keck/NIRC2 using the new infrared pyramid wave front sensor. We detected both PDS 70 b and c in our images, as well as the front rim of the circumstellar disk. After subtracting off a model of the disk, we measured the astrometry and photometry of both planets. Placing priors based on the dynamics of the system, we estimated PDS 70 b to have a semimajor axis of au and PDS 70 c to have a semimajor axis of au (95% credible interval). We fit the spectral energy distribution (SED) of both planets. For PDS 70 b, we were able to place better constraints on the red half of its SED than previous studies and inferred the radius of the photosphere to be 2–3 R Jup. The SED of PDS 70 c is less well constrained, with a range of total luminosities spanning an order of magnitude. With our inferred radii and luminosities, we used evolutionary models of accreting protoplanets to derive a mass of PDS 70 b between 2 and 4 M Jup and a mean mass accretion rate between 3 × 10−7 and 8 × 10−7 M Jup/yr. For PDS 70 c, we computed a mass between 1 and 3 M Jup and mean mass accretion rate between 1 × 10−7 and 5 × 10−7 M Jup/yr. The mass accretion rates imply dust accretion timescales short enough to hide strong molecular absorption features in both planets' SEDs.
|
|
| 3. |
- Absil, Oliver, et al.
(författare)
-
Three years of harvest with the vector vortex coronagraph in the thermal infrared
- 2016
-
Ingår i: Ground-Based and Airborne Instrumentation for Astronomy VI. - : SPIE - International Society for Optical Engineering. - 9781510601963 ; , s. 1-14
-
Konferensbidrag (refereegranskat)abstract
- For several years, we have been developing vortex phase masks based on sub-wavelength gratings, known as Annular Groove Phase Masks. Etched onto diamond substrates, these AGPMs are currently designed to be used in the thermal infrared (ranging from 3 to 13 μm). Our AGPMs were first installed on VLT/NACO and VLT/VISIR in 2012, followed by LBT/LMIRCam in 2013 and Keck/NIRC2 in 2015. In this paper, we review the development, commissioning, on-sky performance, and early scientific results of these new coronagraphic modes and report on the lessons learned. We conclude with perspectives for future developments and applications.
|
|
| 4. |
- Ali, Safdar, et al.
(författare)
-
Electron-ion recombination rate coefficients for C II forming C I
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 753:2, s. 132-
-
Tidskriftsartikel (refereegranskat)abstract
- We have determined absolute dielectronic recombination rate coefficients for C II, using the CRYRING heavy-ions storage ring. The resonances due to 2s-2p (∆n = 0) core excitations are detected in the center-of-mass energy range of 0-15 eV. The experimental results are compared with intermediate coupling AUTOSTRUCTURE calculations. Plasma rate coefficients are obtained from the DR spectrum by convoluting it with a Maxwell-Boltzmann energy distribution for temperatures in the range of 103-106 K. The derived temperature dependent plasma recombination rate coefficients are presented graphically to compare with the theoretical data available in literature and parameterized by using a fit formula for convenient use in plasma modelling codes. In the temperature range of 103-2×104 K, our experimental results show that previous calculations severely underestimate the plasma rate coefficients and also our AUTOSTRUCTURE calculation does not reproduce the experimental plasma rate coefficients well. Above 2×104 K the agreement between the experimental and theoretical rate coefficients is much better, and the deviations are smaller than the estimated uncertainties.
|
|
| 5. |
- Corneille, Olivier, et al.
(författare)
-
POINT OF VIEW Beware ‘persuasive communication devices’ when writing and reading scientific articles
- 2023
-
Ingår i: eLife. - 2050-084X. ; 12
-
Tidskriftsartikel (refereegranskat)abstract
- Authors rely on a range of devices and techniques to attract and maintain the interest of readers, and to convince them of the merits of the author’s point of view. However, when writing a scientific article, authors must use these ‘persuasive communication devices’ carefully. In particular, they must be explicit about the limitations of their work, avoid obfuscation, and resist the temptation to oversell their results. Here we discuss a list of persuasive communication devices and we encourage authors, as well as reviewers and editors, to think carefully about their use.
|
|
| 6. |
- Mahmood, Sultan, et al.
(författare)
-
RECOMBINATION RATE COEFFICIENTS OF BORON-LIKE Ne
- 2013
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 771:2, s. 78-
-
Tidskriftsartikel (refereegranskat)abstract
- Recombination of Ne5+ was measured in a merged-beam type experiment at the heavy-ion storage ring CRYRING. In the collision energy range 0-110 eV resonances due to 2s(2)2p -> 2s2p(2) (Delta n=0) and 2s(2)2p -> 2s(2)3l (Delta n=1), core excitations were observed. The experimentally derived rate coefficients agree well with the calculations obtained using AUTOSTRUCTURE. At low energies, recombination is dominated by resonances belonging to the spin-forbidden 2s2p(2)(P-4(J))nl series. The energy-dependent rate coefficients were convoluted with a Maxwell-Boltzmann electron energy distribution to obtain plasma recombination rate coefficients. The data from the literature deviate from the measured results at low temperature.
|
|
| 7. |
- Orban, Istvan, 1980-, et al.
(författare)
-
Determination of the recombination rate coefficients for Na-like Si IV forming Mg-like Si III
- 2006
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 459:1, s. 291-296
-
Tidskriftsartikel (refereegranskat)abstract
- Aims. Absolute, total recombination rate coefficients for Si IV were determined using the CRYRING heavy-ion storage ring. Calculated rate coefficients were used to estimate recombination into states that could not be detected in the experiment because of field ionization. Total, as well as separate, radiative and dielectronic plasma recombination rate coefficients were determined. Methods. Stored ions were merged with an expanded electron beam in the electron cooler section of the storage ring. Recombined ions were separated from the stored ion beam in the first dipole magnet after the electron cooler and were detected with unity efficiency. The absolute radiative and dielectronic recombination rate coefficients were obtained over a center-of-mass energy range of 0-20 eV, covering Δ n = 0 core excitations up to the 3s → 3d series limit. The results of an intermediate coupling AUTOSTRUCTURE calculation were compared with the experiment. The theoretical results were also used to estimate the contribution to dielectronic recombination by high Rydberg states, which were not detected because of field ionization. The spectra were convoluted with Maxwell-Boltzmann energy distributions in the 103-10 6 K temperature range. Results. The resulting plasma recombination rate coefficients are presented and compared with theoretical results frequently used for plasma modeling. In the 103-104 K range, a significant underestimation of the calculated dielectronic recombination plasma rate coefficients was observed. Above 3 × 104 K, the agreement between our dielectronic recombination plasma rate coefficients and two of the previously published rate coefficients is better than 20%. Conclusions. The observed differences between the experimental and calculated recombination rate coefficients at low temperatures reflect the need for benchmarking experiments. Our experimentally-derived rate coefficients can guide the development of better theoretical models and lead to more accurately-calculated rate coefficients.
|
|
| 8. |
- Orban, Istvan, et al.
(författare)
-
Effects of spin-forbidden resonances on the recombination of Be-like Si and Be-like Ne
- 2011
-
Ingår i: Physica Scripta. - : IOP Publishing Ltd. - 0031-8949 .- 1402-4896. ; T144, s. 014035-
-
Tidskriftsartikel (refereegranskat)abstract
- Recombination through doubly excited states that can be formed only through spin-flip of the excited electrons can give very strong contributions to the recombination rate of Be-like ions. We demonstrate this, in this paper, with the electron-ion recombination spectra of Be-like Ne(6+) and Be-like Si(10+), recently measured at the CRYRING storage ring. These resonances have significant effects on the plasma rate coefficients. We show that neglect or imprecise calculation of these resonances is responsible for large spreads observed between various theoretical results from the literature.
|
|
| 9. |
- Orban, Istvan, 1980-, et al.
(författare)
-
Spectroscopic study of doubly excited states in Mg-like Si using dielectronic recombination
- 2007
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 40:5, s. 1063-1080
-
Tidskriftsartikel (refereegranskat)abstract
- We present calculated and experimentally derived electron-ion recombination rate coefficients for Na-like Si IV, recombining into Mg-like Si III, and provide accurate spectroscopic data for doubly excited states located above the ionization threshold of Si III. The experimental recombination rate coefficients were measured in a merged-beam-type experiment at the heavy-ion storage ring CRYRING at the Manne Siegbahn Laboratory in Stockholm. Changing the electron-ion relative energy from 0 to 20 eV we covered the energy region from the first to the third ionization threshold. We find that even for the low-charged Si2+ ion, a relativistic many-body perturbation theory calculation is necessary, to describe the recombination rate coefficients in the low-energy region, up to 1.5 eV, satisfactorily. Doubly excited states, forbidden to form in LS coupling, are responsible for the most prominent dielectronic recombination resonances at low energies and contribute with 40% to the strength. Several wide resonances give rise to a plateau-like formation in the recombination spectrum. A broader energy range, up to 6.7 eV, was covered with a non-relativistic many-body calculation. This range contains, in addition to 3pnl resonances, several resonances of the type 3dnl, with the LS-forbidden 3d(2) F-3 states giving rise to a strong, isolated peak at 2.976 eV. The NIST database lists eleven doubly excited states of Si III with energy positions deviating considerably from our determination. Since the listed lines are also not fully matching those with the largest fluorescence yields it must be concluded that they are misidentified.
|
|
| 10. |
|
|
