arXiv subjects

E. Tognelli

Publications and source records attributed to E. Tognelli.

At least 19 recordsLinked to original sources

arXiv2025

The growth of a lithium abundance dispersion in pre main sequence stars

Lithium is predicted, and observed, to be depleted in contracting, low-mass pre main sequence (PMS) stars. Yet these stars reach the zero age main sequence (ZAMS) with a spread in lithium abundance at a given effective temperature that is not predicted by standard stellar evolutionary models and which appears to be correlated with rotation. Using a homogeneous dataset provided by the Gaia-ESO spectroscopic survey, we have followed the evolving photospheric lithium content of cohorts of stars destined to be ZAMS late G-, K- and M-dwarfs, in clusters at ages of 2-300 Myr. We show that a dispersion in the LiI 6708A line strength develops in the lower mass stars after 10-20 Myr on the PMS, as soon as Li depletion begins, even in fully convective stars. A model based on a surface starspot coverage varying from star-to-star, leading to a differential Li-burning rate, can explain this temporal behaviour and its mass dependence. However, to fully explain the magnitude of the Li dispersion and its correlation with rotation, the spot coverage during Li-burning would need to be a factor of two larger on average than measured in ZAMS clusters like the Pleiades and continue increasing with rotation in PMS stars beyond the usual "saturation limit" observed for other magnetic activity indicators.

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arXiv2023

AESOPUS 2.0: Low-Temperature Opacities with Solid Grains

In this study we compute the equation of state and Rosseland mean opacity from temperatures of T~30000 K down to T~400 K, pushing the capabilities of the AESOPUS code (Marigo et al., 2022; Marigo & Aringer, 2009) into the regime where solid grains can form. The GGchem code (Woitke et al. 2018) is used to solve the chemistry for temperatures less than ~3000 K. Atoms, molecules, and dust grains in thermodynamic equilibrium are all included in the equation of state. To incorporate monochromatic atomic and molecular cross sections, an optimized opacity sampling technique is used. The Mie theory is employed to calculate the opacity of 43 grain species. Tables of Rosseland mean opacities for scaled-solar compositions are provided. Based on our computing resources, opacities for other chemical patterns, as well as various grain sizes, porosity, and shapes, can be easily computed upon user request to the corresponding author.

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arXiv2022

Low mass young stars in the Milky Way unveiled by DBSCAN and Gaia EDR3. Mapping the star forming regions within 1.5 Kpc

With an unprecedented astrometric and photometric data precision, Gaia EDR3 gives us, for the first time, the opportunity to systematically detect and map in the optical bands, the low mass populations of the star forming regions (SFRs) in the Milky Way. We provide a catalogue of the Gaia EDR3 data (photometry, proper motions and parallaxes) of the young stellar objects (YSOs) identified in the Galactic Plane (|b|<30 deg) within about 1.5 kpc. The catalogue of the SFRs to which they belong is also provided to study the properties of the very young clusters and put them in the context of the Galaxy structure. We applied the machine learning unsupervised clustering algorithm DBSCAN on a sample of Gaia EDR3 data photometrically selected on the region where very young stars (t<10 Myr) are expected to be found, with the aim to identify co-moving and spatially consistent stellar clusters. A subsample of 52 clusters, selected among the 7323 found with DBSCAN, has been used as template data set, to identify very young clusters from the pattern of the observed color-absolute magnitude diagrams through a pattern match process. We find 124440 candidate YSOs clustered in 354 SFRs and stellar clusters younger than 10 Myr and within about 1.5 Kpc. In addition, 65863 low mass members of 322 stellar clusters located within about 500 pc and with ages 10 Myr<t<100 Myr were also found. The selected YSOs are spatially correlated with the well known SFRs. Most of them are associated with well concentrated regions or complex structures of the Galaxy and a substantial number of them have been recognized for the first time. The massive SFRs, such as, for example, Orion, Sco-Cen and Vela, located within 600-700 pc trace a very complex three-dimensional pattern, while the farthest ones seem to follow a more regular pattern along the Galactic Plane.

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arXiv2021

Gaia-ESO Survey: Role of magnetic activity and starspots on pre-main sequence lithium evolution

Pre-main sequence models with inflated radii are needed to simultaneously reproduce the colour-magnitude diagram and the lithium depletion pattern in young open clusters. We tested a new set of PMS models including radius inflation due to starspots or magnetic inhibition of convection, using five clusters observed by the Gaia-ESO Survey, spanning the age range ~10-100 Myr where such effects could be important. Gaia-ESO radial velocities were combined with Gaia EDR3 astrometry to obtain clean lists of high-probability members for the five clusters. A Bayesian maximum likelihood method was adopted to derive the best model parameters and the cluster reddening and age. Models were calculated for different values of the mixing length parameter ($α_{ML}=2.0$, 1.5 and 1.0), without spots or with effective spot coverage $β_{spot}=0.2$ and 0.4. To reproduce the CMD and the Li depletion pattern in Gamma Vel A and B and in 25 Ori we need both a reduced convection efficiency $α_{ML}=1.0$ and an effective spot coverage of ~20%. We obtained ages of 18 Myr and 21 Myr for Gamma Vel A and B, respectively, and 19 Myr for 25 Ori. However, a single isochrone is not sufficient to account for the Li dispersion, and an increasing level of spot coverage as mass decreases seems to be required. The older clusters (NGC2451B at 30 Myr, NGC2547 at 35 Myr, and NGC2516 at 138 Myr) are consistent with standard models ($α_{ML}=2.0$ and no spots) except at low masses: a 20% spot coverage seems to reproduce the sequence of M-type stars better and might explain the observed abundance spread. The quality of Gaia-ESO data combined with Gaia allows us to gain important insights on PMS evolution. Models including starspots can provide a consistent explanation of the cluster sequences and Li abundances of young clusters, although a range of starspot coverage is required to fully reproduce the data.

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arXiv2021

Robust statistical tools for identifying multiple stellar populations in globular clusters in the presence of measurement errors. A case study: NGC 2808

The finding of multiple stellar populations (MP), defined by patterns in the stellar element abundances, is nowadays considered a distinctive feature of globular clusters. However, while data availability and quality improved in last decades, this is not always true for the techniques adopted to their analysis, rising problems of objectivity of the claims and reproducibility. Using NGC 2808 as test case we show the use of well established statistical clustering methods. We focus the analysis to the RGB phase, where two data sets are available from recent literature for low- and high-resolution spectroscopy. We adopt both hierarchical clustering and partition methods. We explicitly address the usually neglected problem of measurement errors. The results of the clustering algorithms were subjected to silhouette width analysis to compare the performance of the split into different number of MP. For both data sets the results are at odd with those reported in the literature. Two MP are detected for both data sets, while the literature reports five and four MP from high- and low-resolution spectroscopy respectively. The silhouette analysis suggests that the population sub-structure is reliable for high-resolution spectroscopy data, while the actual existence of MP is questionable for the low-resolution spectroscopy data. The discrepancy with literature claims is explainable due to the difference of methods adopted to MP characterisation. By means of Monte Carlo simulations and multimodality statistical tests we show that the often adopted study of the histogram of the differences in some key elements is prone to multiple false positive findings. The adoption of statistically grounded methods, which adopt all the available information to subset the data and explicitly address the problem of data uncertainty, is of paramount importance to present more robust and reproducible researches.

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arXiv2021

The Gaia-ESO Survey: Membership probabilities for stars in 63 open and 7 globular clusters from 3D kinematics

Spectroscopy from the final internal data release of the Gaia-ESO Survey (GES) has been combined with Gaia EDR3 to assign membership probabilities to targets observed towards 63 Galactic open clusters and 7 globular clusters. The membership probabilities are based chiefly on maximum likelihood modelling of the 3D kinematics of the targets, separating them into cluster and field populations. From 43211 observed targets, 13985 are identified as highly probable cluster members ($P>0.9$), with an average membership probability of 0.993. The addition of GES radial velocities successfully drives down the fraction of false positives and we achieve better levels of discrimination in most clusters over the use of astrometric data alone, especially those at larger distances. Since the membership selection is almost purely kinematic, the union of this catalogue with GES and Gaia is ideal for investigating the photometric and chemical properties of clusters as a function of stellar mass, age and Galactic position.

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arXiv2021

Theoretical predictions of surface light element abundances in protostellar and pre-Main Sequence phase

Theoretical prediction of surface stellar abundances of light elements -- lithium, beryllium, and boron -- represents one of the most interesting open problems in astrophysics. As well known, several measurements of 7-Li abundances in stellar atmospheres point out a disagreement between predictions and observations in different stellar evolutionary phases, rising doubts about the capability of present stellar models to precisely reproduce stellar envelope characteristics. Light elements are burned at relatively low temperatures (from 2 to 5 MK) and thus in the evolutionary stages of a star they are gradually destroyed at different depths of stellar interior, in dependence on the stellar mass. Their surface abundances are strongly influenced by the nuclear cross sections, by the extension of the convective envelope and by the temperature at its bottom, which depend on the characteristics of the star (mass and chemical composition) as well as on the energy transport in the convective stellar envelope. In recent years, a great effort has been made to improve the precision of light element burning cross sections. However, theoretical predictions surface light element abundance are challenging because they are also influenced by the uncertainties in the input physics adopted in the calculations as well as the efficiency of several standard and non-standard physical processes active in young stars (i.e. diffusion, radiative levitation, magnetic fields, rotation). Moreover, it is still not completely clear how much the previous protostellar evolution affects the characteristics of a stellar model and thus the light element depletion. This paper presents the state-of-the-art of theoretical predictions for protostars and PMS stars, discussing the role of several input physics on the stellar evolution.

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arXiv2021

The Gaia-ESO survey: Mixing processes in low-mass stars traced by lithium abundance in cluster and field stars

We aim to constrain the mixing processes in low-mass stars by investigating the behaviour of the Li surface abundance after the main sequence. We take advantage of the data from the sixth internal data release of Gaia-ESO, idr6, and from the Gaia Early Data Release 3, edr3. We select a sample of main sequence, sub-giant, and giant stars in which Li abundance is measured by the Gaia-ESO survey, belonging to 57 open clusters with ages from 120~Myr to about 7 Gyr and to Milky Way fields, covering a range in [Fe/H] between -1.0 and +0.5dex. We study the behaviour of the Li abundances as a function of stellar parameters. We compare the observed Li behaviour in field giant stars and in giant stars belonging to individual clusters with the predictions of a set of classical models and of models with mixing induced by rotation and thermohaline instability. The comparison with stellar evolution models confirms that classical models cannot reproduce the lithium abundances observed in the metallicity and mass regimes covered by the data. The models that include the effects of both rotation-induced mixing and thermohaline instability account for the Li abundance trends observed in our sample, in all metallicity and mass ranges. The differences between the results of the classical models and of the rotation models largely differ (up to ~2 dex), making lithium the best element to constrain stellar mixing processes in low-mass stars. For stars with well-determined masses, we find a better agreement between observed surface abundances and models with rotation-induced and thermohaline mixings, the former dominating during the main sequence and the first phases of the post-main sequence evolution and the latter after the bump in the luminosity function.

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arXiv2021

Goodness-of-fit test for isochrone fitting in the Gaia era. Statistical assessment of the error distribution

[...] This paper presents a rigorous derivation of a goodness-of-fit statistics for colour-magnitude diagrams (CMD). We discuss the reliability of the underlying assumptions and their validity. We derived the distribution of the sum of squared Mahalanobis distances of stellar data and theoretical isochrone for a generic set of data and models. We applied this to the case of synthetic CMDs constructed to mimic real data of open clusters in the GAIA sample. We analysed the capability of distinguishing among different sets of input physics and parameters that were used to compute the stellar models. We generated synthetic clusters from isochrones computed with these perturbed quantities, and we evaluated the goodness-of-fit with respect to the unperturbed isochrone. We show that when $r$ magnitudes are available for each of the $N$ observational objects and $p$ hyperparameters are estimated in the fit, the error distribution follows a $χ^2$ distribution with $(r-1)N - p$ degrees of freedom. We show that the linearisation of the isochrone causes negligible deviation from this result. We investigated the possibility of detecting the effects on stellar models that are induced when varying convective core overshooting efficiency, $^{14}$N$(p,γ)^{15}$O reaction rate, microscopic diffusion velocities, outer BCs, and colour transformation. The results suggest that it is possible to detect the effect induced by only some of the perturbed quantities. [...] A variation in the convective core overshooting efficiency was detectable only for photometric errors of 0.003 mag and only for the 1 Gyr case. The effects induced by the outer boundary conditions and the bolometric corrections are the largest. [...] As a last exercise, we addressed the validity of the goodness-of-fit statistics for real-world open cluster CMDs, contaminated by field stars or unresolved binaries. [...]

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arXiv2020

Bayesian calibration of the mixing length parameter $α_{ML}$ and of the helium-to-metal enrichment ratio $ΔY/ΔZ$ with open clusters: the Hyades test-bed

We tested the capability of a Bayesian procedure to calibrate both the helium abundance and the mixing length parameter ($α_{ML}$), using precise photometric data for main-sequence (MS) stars in a cluster with negligible reddening and well-determined distance. The method has been applied first to a mock data set generated to mimic Hyades MS stars and then to the real Hyades cluster. We tested the impact on the results of varying the number of stars in the sample, the photometric errors, and the estimated [Fe/H]. The analysis of the synthetic data set shows that $α_{ML}$ is recovered with a very good precision in all the analysed cases (with an error of few percent), while [Fe/H] and the helium-to-metal enrichment ratio $ΔY/ΔZ$ are more problematic. If spectroscopic determinations of [Fe/H] are not available and thus [Fe/H] has to be recovered alongside with $ΔY/ΔZ$ and $α_{ML}$, the well-known degeneracy between [Fe/H]-$ΔY/ΔZ$-$α_{ML}$ could result in a large uncertainty on the recovered parameters, depending on the portion of the MS used for the analysis. On the other hand, the prior knowledge of an accurate [Fe/H] value puts a strong constraint on the models, leading to a more precise parameters recovery. Using the current set of PISA models, the most recent [Fe/H] value and the Gaia photometry and parallaxes for the Hyades cluster, we obtained the average values $<α_{ML}>=2.01\pm0.05$ and $<ΔY/ΔZ>=2.03\pm0.33$, sensitively reducing the uncertainty in these important parameters.

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arXiv2020

On the Metamorphosis of the Bailey diagram for RR Lyrae stars

We collected over 6000 high-resolution spectra of four dozen field RR Lyrae (RRL) variables pulsating either in the fundamental (39 RRab) or in the first overtone (9 RRc) mode. We measured radial velocities (RVs) of four strong metallic and four Balmer lines along the entire pulsational cycle and derived RV amplitudes with accuracies better than 1$-$2~\kmsec. The new amplitudes were combined with literature data for 23~RRab and 3~RRc stars (total sample 74 RRLs) which allowed us to investigate the variation of the Bailey diagram (photometric amplitude versus period) when moving from optical to mid-infrared bands and to re-cast the Bailey diagram in terms of RV amplitudes. We found that RV amplitudes for RRab are minimally affected by nonlinear phenomena (shocks) and multi-periodicity (Blazhko effect). The RV slope ($\log P$--A(V$_r$)) when compared with the visual slope ($\log P$--A($V$)) is shallower and the dispersion, at fixed period, decreases by a factor of two. We constructed homogeneous sets of Horizontal Branch evolutionary models and nonlinear, convective pulsation models of RRLs to constrain the impact of evolutionary effects on their pulsation properties. Evolution causes, on the Bailey diagram based on RV amplitudes, a modest variation in pulsation period and a large dispersion in amplitude. The broad dispersion in period of the Bailey diagram is mainly caused by variation in RRL intrinsic parameters (stellar mass, chemical composition). Empirical evidence indicates that RV amplitudes are an optimal diagnostic for tracing the mean effective temperature across the RRab instability strip.

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arXiv2020

Protostellar accretion in low mass metal poor stars and the cosmological lithium problem

The cosmological lithium problem, that is, the discrepancy between the lithium abundance predicted by the Big Bang nucleosynthesis and the one observed for the stars of the 'Spite plateau', is one of the long standing problems of modern astrophysics. Recent hints for a possible solution involve lithium burning induced by protostellar mass accretion on Spite plateau stars. The purpose of this paper is to analyze the effect of protostellar accretion on low metallicity low-mass stars with a focus on PMS lithium evolution. We computed the evolution from the protostar to the MS phase of accreting models with final masses of 0.7 and 0.8 M$_\odot$, and three metallicities Z=0.0001, Z=0.0010, and Z=0.0050. The effects of changing the main parameters affecting accreting models, that is the accretion energy (cold versus hot accretion), the initial seed mass $M_{seed}$ and radius $R_{seed}$, and the mass accretion rate $\dot{m}$, have been investigated in detail. As for the main stellar properties and the surface $^7 Li$ abundance, hot accretion models converge to standard non-accreting ones within 1 Myr, regardless of the actual value of $M_{seed}$, $R_{seed}$, and $\dot{m}$. Also, cold accretion models with a relatively large $M_{seed}$ ($\gtrsim 10~M_{jup}$) or $R_{seed}$ ($\gtrsim 1~R_\odot$) converge to standard non-accreting ones in less than about 10-20~Myr. A drastically different evolution occurs whenever a cold protostellar accretion process starts from small values of $M_{seed}$ and $R_{seed}$ ($M_{seed}\sim 1~M_{jup}$, $R_{seed} \lesssim 1~R_\odot$). These models almost entirely skip the standard Hayashi track evolution and deplete Li before the end of the accretion phase. The exact amount of depletion depends on the actual combination of the accretion parameters ($\dot{m}$, $M_{seed}$, and $R_{seed}$), achieving in some cases the complete exhaustion of Li in the whole star.

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arXiv2020

Protostellar accretion and the cosmological lithium problem

The cosmological lithium problem, i.e. the discrepancy between the lithium abundance predicted by the Big Bang Nucleosynthesis and the one observed for the stars of the "Spite plateau", is one of the long standing problems of modern astrophysics. A possible astrophysical solution involves lithium burning due to protostellar mass accretion on Spite plateau stars. In present work, for the first time, we investigate with accurate evolutionary computations the impact of accretion on the lithium evolution in the metal-poor regime, that relevant for stars in the Spite plateau.

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arXiv2019

Evidence of a substellar companion to AB Dor C

Studies of fundamental parameters of very low-mass objects are indispensable to provide tests of stellar evolution models that are used to derive theoretical masses of brown dwarfs and planets. However, only objects with dynamically determined masses and precise photometry can effectively evaluate the predictions of stellar models. AB Dor C (0.090 solar masses) has become a prime benchmark for calibration of theoretical evolutionary models of low-mass young stars. One of the ambiguities remaining in AB Dor C is the possible binary nature of this star. We observed AB Dor C with the VLTI/AMBER instrument in low-resolution mode at the J, H and K bands. The interferometric observables at the K-band are compatible with a binary brown dwarf system with tentative components AB Dor Ca/Cb with a K-band flux ratio of 5$\pm$1% and a separation of 38$\pm$1 mas. This implies theoretical masses of 0.072$\pm$0.013 M$_{\rm \odot}$ and 0.013$\pm$0.001 M$_{\rm \odot}$ for each component, near the hydrogen-burning limit for AB Dor Ca, and near the deuterium-burning limit, straddling the boundary between brown dwarfs and giant planets, for AB Dor Cb. The possible binarity of AB Dor C alleviates the disagreement between observed magnitudes and theoretical mass-luminosity relationships.

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arXiv2019

The Gaia-ESO survey: Calibrating a relationship between Age and the [C/N] abundance ratio with open clusters

In the era of large high-resolution spectroscopic surveys, high-quality spectra can contribute to our understanding of the Galactic chemical evolution, providing chemical abundances belonging to the different nucleosynthesis channels, and also providing constraints to stellar age. Some abundance ratios have been proven to be excellent indicators of stellar ages. We aim at providing an empirical relationship between stellar ages and [C/N] using, as calibrators, open star clusters observed by both the Gaia-ESO and APOGEE surveys. We use stellar parameters and abundances from the Gaia-ESO and APOGEE of the Galactic field and open cluster stars. Ages of star clusters are retrieved from the literature sources and validated using a common set of isochrones. We use the same isochrones to determine, for each age and metallicity, the surface gravity at which the first dredge-up and red giant branch bump occur. We study the effect of extra-mixing processes in our sample of giant stars, and we derive the mean [C/N] in evolved stars, including only stars without evidence of extra-mixing. Combining the Gaia-ESO and APOGEE samples of open clusters, we derive a linear relationship between [C/N] and logarithmic cluster ages. We apply our relationship to selected giant field stars in both Gaia-ESO and APOGEE. We find an age separation between thin and thick disc stars and age trends within their populations, with an increasing age towards lower metallicity populations. With such empirical relationship, we are able to provide an age estimate for giant stars in which C and N abundances are measured. Isochrone fitting is less sensitive for giant than dwarf stars at the turn off. The present method can be thus considered as an additional tool to give an independent estimate of the age of giant stars, with uncertainties in their ages comparable to those obtained using isochrone fitting for dwarf stars.

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arXiv2019

The Gaia-ESO Survey: The inner disc, intermediate-age open cluster Pismis 18

Pismis 18 is a moderately populated, intermediate-age open cluster located within the solar circle at a Galactocentric distance of about 7 kpc. Few open clusters have been studied in detail in the inner disc region before the Gaia-ESO Survey. New data from the Gaia-ESO Survey allowed us to conduct an extended radial velocity membership study as well as spectroscopic metallicity and detailed chemical abundance measurements for this cluster. Gaia-ESO Survey data for 142 potential members, lying on the upper MS and on the red clump, yielded radial velocity measurements, which, together with proper motion measurements from the Gaia DR2, were used to determine the systemic velocity of the cluster and membership of individual stars. Photometry from Gaia DR2 was used to re-determine cluster parameters based on high confidence member stars only. Cluster abundance measurements of six radial-velocity member stars with UVES high-resolution spectroscopy are presented for 23 elements. According to the new estimates, based on high confidence members, Pismis 18 has an age of $700^{+40}_{-50}$ Myr, interstellar reddening of E(B-V) = $0.562^{+0.012}_{-0.026}$ mag and a de-reddened distance modulus of $DM_0 = 11.96^{+0.10}_{-0.24}$ mag. The median metallicity of the cluster (using the six UVES stars) is [Fe/H] = $+0.23 \pm 0.05$ dex, with [$α$/Fe]= $0.07 \pm 0.13$ and a slight enhancement of s- and r- neutron-capture elements. With the present work, we fully characterized the open cluster Pismis 18, confirming its present location in the inner disc. We estimated a younger age than the previous literature values and gave, for the first time, its metallicity and its detailed abundances. Its [$α$/Fe] and [s-process/Fe], both slightly super-solar, are in agreement with other inner-disc open clusters observed by the Gaia-ESO survey. [abridged]

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arXiv2019

The Gaia-ESO Survey: age spread in the star forming region NGC6530 from the HR diagram and gravity indicators

In very young clusters, stellar age distribution is the empirical proof of the duration of star formation (SF) and of the physical mechanisms involved in the process. We derived accurate stellar ages for the cluster NGC6530, associated with the Lagoon Nebula to infer its SF history. We use the Gaia-ESO survey observations and Gaia DR2 data, to derive cluster membership and fundamental stellar parameters. We identified 652 confirmed and 9 probable members. The reddening inferred for members and non-members allows us to distinguish MS stars and giants, in agreement with the distances inferred from Gaia DR2 data. The foreground and background stars show a spatial pattern that traces the 3D structure of the nebular dust component. We derive stellar ages for 382 confirmed cluster members and we find that the gravity-sensitive gamma index distribution for M stars is correlated with stellar age. For all members with Teff<5500 K, the mean logarithmic age is 5.84 (units of years) with a dispersion of 0.36 dex. The age distribution of stars with accretion and/or disk (CTTSe) is similar to that of stars without accretion and without disk (WTTSp). We interpret this dispersion as evidence of a real age spread since the total uncertainties on age determinations, derived from Monte Carlo simulations, are significantly smaller than the observed spread. This conclusion is supported by the evidence of a decreasing of the gravity-sensitive gamma index as a function of stellar ages. The presence of the age spread is also supported by the spatial distribution and the kinematics of old and young members. In particular, members with accretion and/or disk, formed in the last 1 Myr, show evidence of subclustering around the cluster center, in the Hourglass Nebula and in the M8-E region, suggesting a possible triggering of star formation events by the O-type star ionization fronts.

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arXiv2018

Investigating the population of Galactic star formation regions and star clusters within a Wide-Fast-Deep Coverage of the Galactic Plane

One of the aims of LSST is to perform a systematic survey of star clusters and star forming regions (SFRs) in our Galaxy. In particular, the observations obtained with LSST will make a big difference in Galactic regions that have been poorly studied in the past, such as the anticenter and the disk beyond the Galactic center, and they will have a strong impact in discovering new distant SFRs. These results can be achieved by exploiting the exquisite depth that will be attained if the wide-fast-deep (WFD) observing strategy of the main survey is also adopted for the Galactic plane, in the g, r, and i filters.

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