arXiv subjects

P. Grani

Publications and source records attributed to P. Grani.

4 recordsLinked to original sources

arXiv2026

The VLT/ERIS grating vector Apodizing Phase Plate coronagraph

We describe the design, laboratory manufacture, and on-sky testing of the grating vector apodizing phase plate (gvAPP) coronagraph for the Enhanced Resolution Imager and Spectrograph (ERIS) on the Very Large Telescope. We used both laboratory measurements and on-sky observations to characterise the gvAPP in several different filters, from the K to the L band. In testing, the gvAPP reaches its design specification in the transmission of the optic with 90% in the K bands and 60% in the L band. While the gvAPP reaches its designed raw contrast performance of $1 \times 10^{-5}$, it does not reach the post-processed contrast of $5 \times 10^{-5}$ in on-sky observations. Electronic detector noise, due to the Airy core of the coronagraphic point spread function inducing cross-talk between the readout amplifiers, produces a repeated pattern within the coronagraphic regions of the gvAPP. Despite these limitations, we recommend the gvAPP as a tool for characterising substellar companions with known separations and position angles, which allow them to be placed in the coronagraphic dark holes for observations. The ERIS gvAPP's leakage term can also be used as a photometric reference for time series observations; however, we caution that the contrast performance may limit such studies to only the brightest targets. ERIS gvAPP data quality may be improved further with better modelling of detector electronic noise. This work is a pathfinder for Extremely Large Telescope instruments including METIS, which will include gvAPP coronagraphs with improved designs based on these results.

astro-ph.IM↗

arXiv2025

The gas streamer G1-2-3 in the Galactic Center

The black hole in the Galactic Center, Sgr A*, is prototypical for ultra-low-fed galactic nuclei. The discovery of a hand-full of gas clumps in the realm of a few Earth masses in its immediate vicinity provides a gas reservoir sufficient to power Sgr A*. In particular, the gas cloud G2 is of interest due to its extreme orbit, on which it passed at a pericenter distance of around 100 AU and notably lost kinetic energy during the fly-by due to the interaction with the black hole accretion flow. 13 years prior to G2, a resembling gas cloud called G1, passed Sgr A* on a similar orbit. The origin of G2 remained a topic of discussion, with models including a central (stellar) source still proposed as alternatives to pure gaseous clouds. Here, we report the orbit of a third gas clump moving again along (almost) the same orbital trace. Since the probability of finding three stars on close orbits is very small, this strongly argues against stellar-based source models. Instead, we show that the gas streamer G1-2-3 plausibly originates from the stellar wind of the massive binary star IRS16SW. This claim is substantiated by the fact that the small differences between the three orbits - the orientations of the orbital ellipses in their common plane as a function of time - are consistent with the orbital motion of IRS 16SW.

astro-ph.GA↗

arXiv2023

GMP-selected dual and lensed AGNs: selection function and classification based on near-IR colors and resolved spectra from VLT/ERIS, KECK/OSIRIS, and LBT/LUCI

The Gaia-Multi-Peak (GMP) technique can be used to identify large numbers of dual or lensed AGN candidates at sub-arcsec separation, allowing us to study both multiple SMBHs in the same galaxy and rare, compact lensed systems. The observed samples can be used to test the predictions of the models of SMBH merging once 1) the selection function of the GMP technique is known, and 2) each system has been classified as dual AGN, lensed AGN, or AGN/star alignment. Here we show that the GMP selection is very efficient for separations above 0.15'' when the secondary (fainter) object has magnitude G<20.5. We present the spectroscopic classification of five GMP candidates using VLT/ERIS and Keck/OSIRIS, and compare them with the classifications obtained from: a) the near-IR colors of 7 systems obtained with LBT/LUCI, and b) the analysis of the total, spatially-unresolved spectra. We conclude that colors and integrated spectra can already provide reliable classifications of many systems. Finally, we summarize the confirmed dual AGNs at z>0.5 selected by the GMP technique, and compare this sample with other such systems from the literature, concluding that GMP can provide a large number of confirmed dual AGNs at separations below 7 kpc.

astro-ph.GA↗

arXiv2023

The Enhanced Resolution Imager and Spectrograph for the VLT

ERIS, the Enhanced Resolution Imager and Spectrograph, is an instrument that both extends and enhances the fundamental diffraction limited imaging and spectroscopy capability for the VLT. It replaces two instruments that were being maintained beyond their operational lifetimes, combines their functionality on a single focus, provides a new wavefront sensing module for natural and laser guide stars that makes use of the Adaptive Optics Facility, and considerably improves on their performance. The observational modes ERIS provides are integral field spectroscopy at 1-2.5 {\mu}m, imaging at 1-5 {\mu}m with several options for high contrast imaging, and longslit spectroscopy at 3-4 {\mu}m, The instrument is installed at the Cassegrain focus of UT4 at the VLT and, following its commissioning during 2022, has been made available to the community.

astro-ph.IM↗