13 research outputs found
The transitional gap transient AT 2018hso: new insights into the luminous red nova phenomenon
Context. The absolute magnitudes of luminous red novae (LRNe) are intermediate between those of novae and supernovae (SNe), and show a relatively homogeneous spectro-photometric evolution. Although they were thought to derive from core instabilities in single stars, there is growing support for the idea that they are triggered by binary interaction that possibly ends with the merging of the two stars.
Aims. AT 2018hso is a new transient showing transitional properties between those of LRNe and the class of intermediate-luminosity red transients (ILRTs) similar to SN 2008S. Through the detailed analysis of the observed parameters, our study supports that it actually belongs to the LRN class and was likely produced by the coalescence of two massive stars.
Methods. We obtained ten months of optical and near-infrared photometric monitoring, and 11 epochs of low-resolution optical spectroscopy of AT 2018hso. We compared its observed properties with those of other ILRTs and LRNe. We also inspected the archival Hubble Space Telescope (HST) images obtained about 15 years ago to constrain the progenitor properties.
Results. The light curves of AT 2018hso show a first sharp peak (reddening-corrected M-r = -13.93 mag), followed by a broader and shallower second peak that resembles a plateau in the optical bands. The spectra dramatically change with time. Early-time spectra show prominent Balmer emission lines and a weak [Ca II] doublet, which is usually observed in ILRTs. However, the strong decrease in the continuum temperature, the appearance of narrow metal absorption lines, the great change in the H alpha strength and profile, and the emergence of molecular bands support an LRN classification. The possible detection of a M-I similar to -8 mag source at the position of AT 2018hso in HST archive images is consistent with expectations for a pre-merger massive binary, similar to the precursor of the 2015 LRN in M101.
Conclusions. We provide reasonable arguments to support an LRN classification for AT 2018hso. This study reveals growing heterogeneity in the observables of LRNe than has been thought previously, which is a challenge for distinguishing between LRNe and ILRTs. This suggests that the entire evolution of gap transients needs to be monitored to avoid misclassifications
North-PHASE : Studying periodicity, hot spots, accretion stability and early evolution in young stars in the northern hemisphere
Funding: RK is funded by the STFC under grant number ST/W507404/1. LS was funded by the RAS Undergraduate Summer Bursary. VR acknowledges the support of the Italian National Institute of Astrophysics (INAF) through the INAF GTO Grant ‘ERIS & SHARK GTO data exploitation’ and the European Union’s Horizon 2020 research and innovation program and the European Research Council via the ERC Synergy Grant ‘ECOGAL’ (project ID 855130). JCW and CM are Funded by the European Union (ERC, WANDA, 101039452).We present the overview and first results from the North-PHASE Legacy Survey, which follows six young clusters for five years, using the 2 deg2 FoV of the JAST80 telescope from the Javalambre Observatory (Spain). North-PHASE investigates stellar variability on timescales from days to years for thousands of young stars distributed over entire clusters. This allows us to find new YSO, characterise accretion and study inner disk evolution within the cluster context. Each region (Tr 37, Cep OB3, IC 5070, IC 348, NGC 2264, and NGC 1333) is observed in six filters (SDSS griz, u band, and J0660, which covers Hα), detecting cluster members as well as field variable stars. Tr 37 is used to prove feasibility and optimise the variability analysis techniques. In Tr 37, variability reveals 50 new YSO, most of them proper motion outliers. North-PHASE independently confirms the youth of astrometric members, efficiently distinguishes accreting and non-accreting stars, reveals the extent of the cluster populations along Tr37/IC 1396 bright rims, and detects variability resulting from rotation, dips, and irregular bursts. The proper motion outliers unveil a more complex star formation history than inferred from Gaia alone, and variability highlights previously hidden proper motion deviations in the surrounding clouds. We also find that non-YSO variables identified by North-PHASE cover a different variability parameter space and include long-period variables, eclipsing binaries, RR Lyr, and δ Scuti stars. These early results also emphasize the power of variability to complete the picture of star formation where it is missed by astrometry.Peer reviewe
J-PLUS DR3: Galaxy-Star-Quasar classification
The Javalambre Photometric Local Universe Survey (J-PLUS) is a 12-band
photometric survey using the 83-cm JAST telescope. Data Release 3 includes 47.4
million sources (29.8 million with ) on 3192 deg (2881 deg
after masking). J-PLUS DR3 only provides star-galaxy classification so that
quasars are not identified from the other sources. Given the size of the
dataset, machine learning methods could provide a valid alternative
classification and a solution to the classification of quasars. Our objective
is to classify J-PLUS DR3 sources into galaxies, stars and quasars,
outperforming the available classifiers in each class. We use an automated
machine learning tool called {\tt TPOT} to find an optimized pipeline to
perform the classification. The supervised machine learning algorithms are
trained on the crossmatch with SDSS DR12, LAMOST DR7 and \textit{Gaia} DR3. We
checked that the training set of about 570 thousand galaxies, one million stars
and 220 thousand quasars is both representative and pure to a good degree. We
considered 37 features: besides the twelve photometric bands with their errors,
six colors, four morphological parameters, galactic extinction with its error
and the PSF relative to the corresponding pointing. After exploring numerous
pipeline possibilities through the TPOT genetic algorithm, we found that
XGBoost provides the best performance: the AUC for galaxies, stars and quasars
is above 0.99 and the average precision is above 0.99 for galaxies and stars
and 0.94 for quasars. XGBoost outperforms the star-galaxy classifiers already
provided in J-PLUS DR3 and also efficiently classifies quasars. We also found
that photometry was very important in the classification of quasars, showing
the relevance of narrow-band photometry.Comment: 14 pages, 17 figure
The transitional gap transient AT 2018hso: new insights into the luminous red nova phenomenon
Context. The absolute magnitudes of luminous red novae (LRNe) are
intermediate between those of novae and supernovae (SNe), and show a
relatively homogeneous spectro-photometric evolution. Although they were
thought to derive from core instabilities in single stars, there is
growing support for the idea that they are triggered by binary
interaction that possibly ends with the merging of the two stars. Aims: AT 2018hso
is a new transient showing transitional properties between those of
LRNe and the class of intermediate-luminosity red transients (ILRTs)
similar to SN 2008S. Through the detailed analysis of
the observed parameters, our study supports that it actually belongs to
the LRN class and was likely produced by the coalescence of two massive
stars. Methods: We obtained ten months of optical and
near-infrared photometric monitoring, and 11 epochs of low-resolution
optical spectroscopy of AT 2018hso. We compared its
observed properties with those of other ILRTs and LRNe. We also
inspected the archival Hubble Space Telescope (HST) images obtained
about 15 years ago to constrain the progenitor properties. Results: The light curves of AT 2018hso show a first sharp peak (reddening-corrected Mr
= -13.93 mag), followed by a broader and shallower second peak that
resembles a plateau in the optical bands. The spectra dramatically
change with time. Early-time spectra show prominent Balmer emission
lines and a weak [Ca II] doublet, which is usually observed in ILRTs.
However, the strong decrease in the continuum temperature, the
appearance of narrow metal absorption lines, the great change in the Hα
strength and profile, and the emergence of molecular bands support an
LRN classification. The possible detection of a MI ̃ -8 mag source at the position of AT 2018hso
in HST archive images is consistent with expectations for a pre-merger
massive binary, similar to the precursor of the 2015 LRN in M101. Conclusions: We provide reasonable arguments to support an LRN classification for AT 2018hso.
This study reveals growing heterogeneity in the observables of LRNe
than has been thought previously, which is a challenge for
distinguishing between LRNe and ILRTs. This suggests that the entire
evolution of gap transients needs to be monitored to avoid
misclassifications. The light curves and the reduced spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/632/L6</a
A long life of excess: The interacting transient SN 2017hcc
In this study we present the results of a five-year follow-up campaign of the
long-lived type IIn supernova SN 2017hcc, found in a spiral dwarf host of
near-solar metallicity. The long rise time (57 2 days, ATLAS band)
and high luminosity (peaking at 20.78 0.01 mag in the ATLAS band)
point towards an interaction of massive ejecta with massive and dense
circumstellar material (CSM). The evolution of SN 2017hcc is slow, both
spectroscopically and photometrically, reminiscent of the long-lived type IIn,
SN 2010jl. An infrared (IR) excess was apparent soon after the peak, and
blueshifts were noticeable in the Balmer lines starting from a few hundred
days, but appeared to be fading by around +1200 days. We posit that an IR light
echo from pre-existing dust dominates at early times, with some possible
condensation of new dust grains occurring at epochs >+800 days.Comment: Accepted to A&
North-PHASE: Studying Periodicity, Hot Spots, Accretion Stability and Early Evolution in young stars in the northern hemisphere
We present the overview and first results from the North-PHASE Legacy Survey, which follows six young clusters for five years, using the 2 deg2 FoV of the JAST80 telescope from the Javalambre Observatory (Spain). North-PHASE investigates stellar variability on timescales from days to years for thousands of young stars distributed over entire clusters. This allows us to find new YSO, characterise accretion and study inner disk evolution within the cluster context. Each region (Tr 37, Cep OB3, IC 5070, IC 348, NGC 2264, and NGC 1333) is observed in six filters (SDSS griz, u band, and J0660, which covers Hα), detecting cluster members as well as field variable stars. Tr 37 is used to prove feasibility and optimise the variability analysis techniques. In Tr 37, variability reveals 50 new YSO, most of them proper motion outliers. North-PHASE independently confirms the youth of astrometric members, efficiently distinguishes accreting and non-accreting stars, reveals the extent of the cluster populations along Tr37/IC 1396 bright rims, and detects variability resulting from rotation, dips, and irregular bursts. The proper motion outliers unveil a more complex star formation history than inferred from Gaia alone, and variability highlights previously hidden proper motion deviations in the surrounding clouds. We also find that non-YSO variables identified by North-PHASE cover a different variability parameter space and include long-period variables, eclipsing binaries, RR Lyr, and δ Scuti stars. These early results also emphasize the power of variability to complete the picture of star formation where it is missed by astrometry
Costs and benefits of automation for astronomical facilities
The Observatorio Astrof\'isico de Javalambre (OAJ{\dag}1) in Spain is a young
astronomical facility, conceived and developed from the beginning as a fully
automated observatory with the main goal of optimizing the processes in the
scientific and general operation of the Observatory. The OAJ has been
particularly conceived for carrying out large sky surveys with two
unprecedented telescopes of unusually large fields of view (FoV): the JST/T250,
a 2.55m telescope of 3deg field of view, and the JAST/T80, an 83cm telescope of
2deg field of view. The most immediate objective of the two telescopes for the
next years is carrying out two unique photometric surveys of several thousands
square degrees, J-PAS{\dag}2 and J-PLUS{\dag}3, each of them with a wide range
of scientific applications, like e.g. large structure cosmology and Dark
Energy, galaxy evolution, supernovae, Milky Way structure, exoplanets, among
many others. To do that, JST and JAST are equipped with panoramic cameras under
development within the J-PAS collaboration, JPCam and T80Cam respectively,
which make use of large format (~ 10k x 10k) CCDs covering the entire focal
plane. This paper describes in detail, from operations point of view, a
comparison between the detailed cost of the global automation of the
Observatory and the standard automation cost for astronomical facilities, in
reference to the total investment and highlighting all benefits obtained from
this approach and difficulties encountered. The paper also describes the
engineering development of the overall facilities and infrastructures for the
fully automated observatory and a global overview of current status,
pinpointing lessons learned in order to boost observatory operations
performance, achieving scientific targets, maintaining quality requirements,
but also minimizing operation cost and human resources.Comment: Global Observatory Control System GOC
The Wide-field Spectroscopic Telescope (WST) Science White Paper
The Wide-field Spectroscopic Telescope (WST) is proposed as a new facility dedicated to the efficient delivery of spectroscopic surveys. This white paper summarises the initial concept as well as the corresponding science cases. WST will feature simultaneous operation of a large field-of-view (3 sq. degree), a high multiplex (20,000) multi-object spectrograph (MOS) and a giant 3x3 sq. arcmin integral field spectrograph (IFS). In scientific capability these requirements place WST far ahead of existing and planned facilities. Given the current investment in deep imaging surveys and noting the diagnostic power of
spectroscopy, WST will fill a crucial gap in astronomical capability and work synergistically with future ground and space-based facilities. This white paper shows that WST can address outstanding scientific questions in the areas of cosmology; galaxy assembly, evolution, and enrichment, including our own Milky Way; origin of stars and planets; time domain and multi-messenger astrophysics. WST's uniquely rich dataset will deliver unforeseen discoveries in many of these areas. The WST Science Team (already including more than 500 scientists worldwide) is open to the all astronomical community. To register in the WST Science Team please visit https://www.wstelescope.com/for-scientists/participat
Revealing the population of the young ASCC 20
International audienceWe present the study of the open cluster ASCC-20. This young stellar association located at 450 pc and A_V = 0.129 mag is ˜ 20 Myr old based on the upper main sequence fitting. We have created a multi-wavelength photometric catalogue of cluster candidate members by using archival data and data-mining techniques. The complete set of photometric bands contains: B_TV_T from Tycho-2, griz from SDSS, JHK_s from 2MASS and W1W2W3W4 from WISE. In addition, we have followed-up 36 of our photometric candidates by using spectroscopic data with CAHA-TWIN. We have derived spectral types and confirmed their membership: 1) 50% of these sources are M dwarfs with the Hα spectral feature in emission; 2) models (Allard et al., 2012) indicate a mass of ˜0.25 M_{⊙} for the faintest object confirmed by spectroscopy, a M7. We have re-observed a subsample of 11 confirmed members of M spectral type and measured features related with their youth (e.g.: Li at 6707.8 Å) and metallicities by using GTC-OSIRIS at mid-resolution. Assuming a distance of 450 pc we report a Lithium Depletion Boundary age above 30 Myr, based on the faintest member of our sample without lithium (a M7). However a new study of the distance with Gaia will release a new insigth in the age of this cluster