arXiv subjects

Andrea Serio

Publications and source records attributed to Andrea Serio.

5 recordsLinked to original sources

arXiv2026

A SPHEREx Pipeline and Spectral Library for Ultracool Dwarfs

We present a Python spectrophotometry extraction tool tailored for fast-moving point sources detected in the SPHEREx mission, and use it to construct a set of 0.75-5.0 $\mu$m low-resolution ($\lambda/\Delta\lambda \sim 50$) spectrophotometry data products based on the SPHEREx Quick Release 2 (QR2) for a set of 6003 L0-Y1 ultracool dwarfs: 2050 known ultracool dwarfs, 3008 known photometric ultracool dwarf candidates, and 947 newly identified ultracool dwarfs. This work more than doubles the number of ultracool dwarfs with spectroscopy, from 3449 to 7402. We provide SPHEREx templates for each spectral subtype and a set of tools to assign automated spectral types. The QR2 data release generates spectrophotometry with an average signal-to-noise per spectral channel above $\sim$10 for most objects with WISE W2 magnitudes of 14.0 mag and brighter. The compiled data set is made available publicly at https://mocadb.ca, where new spectral compilations from future data releases will also be made available as they are published. These new data provide a significant increase in the number of substellar objects for which the 2.4-5.0 $\mu$m window is now accessible, making it possible to probe important molecular chemistry of key CNOS-bearing species for the coolest brown dwarfs. We flag 2668 ultracool dwarfs as candidate young brown dwarfs, 250 as candidate subdwarfs, and 865 as possibly otherwise peculiar for future investigation. The SPIFF library presented here opens the doors to efficient confirmation of candidate substellar objects and follow-up studies of population-level atmospheric properties of cold brown dwarfs.

astro-ph.SR↗

arXiv2026

Three Thousand Motion-Confirmed L and T Dwarf Candidates from the Backyard Worlds:~Planet 9 Citizen Science Project

The Backyard Worlds: Planet 9 citizen science project uses data from the Wide-field Infrared Survey Explorer to detect infrared objects with significant motion. In this work, we present the majority of the L and T dwarf candidates discovered through this effort. For each candidate, we provide proper motion measurements as well as optical, near-infrared, and mid-infrared photometry (when available), photometric spectral types and distance estimates. Three thousand and six new motion-confirmed discoveries are presented in this work, 2,357 with L-type photometric spectral types and 649 with T-type photometric spectral types. We also present an additional 80 objects as likely L or T dwarfs based on available photometry, but for which a significant motion measurement could not be obtained. We identify 28 objects in this sample as new comoving companions to higher-mass stars, and an additional 9 sources that are candidate binary systems made up of two ultracool dwarfs of L-type or later. Follow-up spectroscopic observations will be necessary to confirm spectral types and further characterize the sources discovered through this project. This work presents the largest single sample of motion-confirmed L and T dwarf discoveries to date, which would more than double the number of known L and T dwarfs, if confirmed. We wish to sincerely thank our citizen scientist collaborators for their monumental efforts that have directly impacted this project's success.

astro-ph.SR↗

arXiv2023

Spectral minimal partitions of unbounded metric graphs

We investigate the existence or non-existence of spectral minimal partitions of unbounded metric graphs, where the operator applied to each of the partition elements is a Schrödinger operator of the form $-Δ+ V$ with suitable (electric) potential $V$, which is taken as a fixed, underlying ``landscape'' on the whole graph. We show that there is a strong link between spectral minimal partitions and infimal partition energies on the one hand, and the infimum $Σ$ of the essential spectrum of the corresponding Schrödinger operator on the whole graph on the other. Namely, we show that for any $k\in\mathbb{N}$, the infimal energy among all admissible $k$-partitions is bounded from above by $Σ$, and if it is strictly below $Σ$, then a spectral minimal $k$-partition exists. We illustrate our results with several examples of existence and non-existence of minimal partitions of unbounded and infinite graphs, with and without potentials. The nature of the proofs, a key ingredient of which is a version of Persson's theorem for quantum graphs, strongly suggests that corresponding results should hold for Schrödinger operator-based partitions of unbounded domains in Euclidean space.

math.SP↗

arXiv2020

On extremal eigenvalues of the graph Laplacian

Upper and lower estimates of eigenvalues of the Laplacian on a metric graph have been established in 2017 by G. Berkolaiko, J.B. Kennedy, P. Kurasov and D. Mugnolo. Both these estimates can be achieved at the same time only by highly degenerate eigenvalues which we call maximally degenerate. By comparison with the maximal eigenvalue multiplicity proved by I. Kac and V. Pivovarchik in 2011 we characterize the family of graphs exhibiting maximally degenerate eigenvalues which we call lasso trees, namely graphs constructed from trees by attaching lasso graphs to some of the vertices.

math.SP↗

arXiv2020

Concrete method for recovering the Euler characteristic of quantum graphs

Trace formulas play a central role in the study of spectral geometry and in particular of quantum graphs. The basis of our work is the result by Kurasov which links the Euler characteristic $χ$ of metric graphs to the spectrum of their standard Laplacian. These ideas were shown to be applicable even in an experimental context where only a finite number of eigenvalues from a physical realization of quantum graph can be measured. In the present work we analyse sufficient hypotheses which guarantee the successful recovery of $χ$. We also study how to improve the efficiency of the method and in particular how to minimise the number of eigenvalues required. Finally, we compare our findings with numerical examples---surprisingly, just a few dozens of eigenvalues can be enough.

math.SP↗