COIN-Focus #4: SPICY – France – 2022
The SPICY project was one of the results from COIN Residence Program #6 (CRP6), which took place in Chamonix, France, August/2019. It consisted of a catalog of young stellar objects (YSO) automatically identified using machine
COIN-Focus #2: Toliman – Rome, Italy – 2019
The COIN-Focus Toliman edition is a collaborative effort to discuss and develop methodological data analysis strategies that will make possible the TOLIMAN mission of detecting habitable exoplanets around our nearest stars. The team is formed by researchers from both collaborations working together in the design of a joint signal-processing and statistical inference system to enable the detection of exoplanets from diffractive pupil based relative astrometry from space.
COIN-Focus #1: RESSPECT – France – 2019
The Cosmostatistics Initiative (COIN) is an international network which aims to create an interdisciplinary environment where collaborations between astronomers, statisticians and machine learning experts can flourish. The group utilizes a management model which can find parallel in technological start-ups: based on a dynamic, non-hierarchical and people-centric approach.
ELEPHANT: ExtragaLactic alErt Pipeline for Hostless AstroNomical Transients
ELEPHANT represents an effective strategy to filter extragalactic events within large and complex astronomical alert streams. There are many applications for which this pipeline will be useful, ranging from transient selection for follow-up to studies of transient environments. We find that less than 2% of all analyzed transients are potentially hostless. Among them, approximately 10% have a spectroscopic class reported on TNS, with Type Ia supernova being the most common class, followed by SLSN. Among the hostless candidates retrieved by our pipeline, there was SN 2018ibb, which has been proposed to be a PISN candidate; and SN 2022ann, one of only five known SNe Icn. When no class is reported on TNS, the dominant classes are QSO and SN candidates, the former obtained from SIMBAD and the latter inferred using the Fink ML classifier.
Are classification metrics good proxies for SN Ia cosmological constraining power?
We emulate photometric SN Ia cosmology samples with controlled contamination rates of individual contaminant classes and evaluate each of them under a set of classification metrics. We then derive cosmological parameter constraints from all samples under two common analysis approaches and quantify the impact of contamination by each contaminant class on the resulting cosmological parameter estimates. We observe that cosmology metrics are sensitive to both the contamination rate and the class of the contaminating population, whereas the classification metrics are insensitive to the latter. We therefore discourage exclusive reliance on classification-based metrics for cosmological analysis design decisions, e.g. classifier choice, and instead recommend optimizing using a metric of cosmological parameter constraining power.
A graph-based spectral classification of SN-II
This work presents new data-driven classification heuristics for spectral data based on graph theory. As a case in point, we devise a spectral classification scheme of Type II supernova (SNe II) as a function of the phase relative to the V -band maximum light and the end of the plateau phase. Our classification method naturally identifies outliers and arranges the different SNe in terms of their major spectral features. The automated classification naturally reflects the fast evolution of Type II SNe around the maximum light while showcasing their homogeneity close to the end of the plateau phase. The scheme we develop could be more widely applicable to unsupervised time series classification or characterization of other functional data.
Spectroscopic Confirmation of a population of Isolated, Intermediate-Mass YSOs
The Spitzer/IRAC Candidate YSO (SPICY) catalog is one of the largest compilations of such objects (~120,000 candidates in the Galactic midplane). Many SPICY candidates are spatially clustered, but, perhaps surprisingly, approximately half the candidates appear spatially distributed. To better characterize this unexpected population and confirm its nature, we obtained Palomar/DBSP spectroscopy for 26 of the optically-bright (G<15 mag) "isolated" YSO candidates. We confirm the YSO classifications of all 26 sources based on their positions on the Hertzsprung-Russell diagram, H and Ca II line-emission from over half the sample, and robust detection of infrared excesses. This implies a contamination rate of <10% for SPICY stars that meet our optical selection criteria.
A high pitch angle structure in the Sagittarius Arm
We map the 3D locations and velocities of star-forming regions in a segment of the Sagittarius Arm using young stellar objects (YSOs) from the Spitzer/IRAC Candidate YSO (SPICY) catalog to compare their distribution to models of the arm. Distances and velocities for these objects are derived from Gaia EDR3 astrometry and molecular line surveys. We infer parallaxes and proper motions for spatially clustered groups of YSOs and estimate their radial velocities from the velocities of spatially associated molecular clouds. The observed 56◦ pitch angle is remarkably high for a segment of the Sagittarius Arm. We discuss possible interpretations of this feature as a substructure within the lower pitch angle Sagittarius Arm, as a spur, or as an isolated structure.
Dawn of Stars
Dawn of Stars tells the story of how stars are formed. Most stars are born in groups which are truly stellar nurseries composed by clouds of dust and gas. This birth process is full of episodes, some of which are represented musically in the four parts of this piece. This was the first art-related project to be developed by COIN, in March 2021, in collaboration with Rodrigo Roriz Teodoro, as part of his graduation project to obtain the degree of Master in music composition awarded by the Marshall University (USA).
SPICY: The Spitzer/IRAC Candidate YSO Catalog
We present ~120,000 candidate young stellar objects (YSOs) based on surveys of the Galactic midplane between l ∼ 255° and 110°, including the GLIMPSE I, II, and 3D, Vela-Carina, Cygnus X, and SMOG surveys (613 square degrees), augmented by near-infrared catalogs. We employed a classification scheme that uses the flexibility of a tailored statistical learning method and curated YSO datasets to take full advantage of IRAC’s spatial resolution and sensitivity in the mid-infrared ∼3–9 μm range. We also identify areas of IRAC color space associated with objects with strong silicate absorption or polycyclic aromatic hydrocarbon emission. Spatial distributions and variability properties help corroborate the youthful nature of our sample.