arXiv subjects

Luisa Rebull

Publications and source records attributed to Luisa Rebull.

At least 19 recordsLinked to original sources

arXiv2025

Dangerous Questions in Astronomy Education

As astronomy enters an era defined by global telescope networks, petabyte-scale surveys, and powerful computational tools, the longstanding goals of astronomy education, particularly introductory ``ASTRO101'', but equally encompassing both higher and lower level courses, warrant fresh examination. In June 2024, the AstroEdUNC meeting at UNC--Chapel Hill convened 100 astronomers, education researchers, and practitioners to synthesise community perspectives on the purpose, content, and delivery of astronomy education. Beginning with historical vignettes, the meeting's deliberations were organised into six interrelated themes: (1) Context, highlighting astronomy's evolution from classical charting to multi-messenger discovery and its role as a connective thread across STEM and the humanities; (2) Content, exploring how curricula can balance essential concepts with authentic investigations and leverage open-source and AI-augmented resources; (3) Skills, arguing that astronomy should foreground scientific literacy, computational fluency, and communication through genuine data-driven inquiry; (4) Engagement, advocating for active-learning strategies, formative assessment, and culturally inclusive narratives; (5) Beyond the Classroom, emphasising scaffolding, universal-design practices, and K--12/community partnerships; and (6) Astronomy Education Research, outlining priority areas for assessing knowledge, attitudes, and long-term outcomes. We provide concrete recommendations for future astronomy education research development, underscoring the need for approaches to education that are authentic while meeting the learning and life goal needs of the students, a vibrant community of practice and robust researcher-practitioner partnerships to ensure that introductory astronomy is pertinent, applicable and inspiring to a broad student population.

physics.ed-ph↗

arXiv2023

Assessing your Observatory's Impact: Best Practices in Establishing and Maintaining Observatory Bibliographies

Observatories need to measure and evaluate the scientific output and overall impact of their facilities. An observatory bibliography consists of the papers published using that observatory's data, typically gathered by searching the major journals for relevant keywords. Recently, the volume of literature and methods by which the publications pool is evaluated has increased. Efficient and standardized procedures are necessary to assign meaningful metadata; enable user-friendly retrieval; and provide the opportunity to derive reports, statistics, and visualizations to impart a deeper understanding of the research output. In 2021, a group of observatory bibliographers from around the world convened online to continue the discussions presented in Lagerstrom (2015). We worked to extract general guidelines from our experiences, techniques, and lessons learnt. The paper explores the development, application, and current status of telescope bibliographies and future trends. This paper briefly describes the methodologies employed in constructing databases, along with the various bibliometric techniques used to analyze and interpret them. We explain reasons for non-standardization and why it is essential for each observatory to identify metadata and metrics that are meaningful for them; caution the (over-)use of comparisons among facilities that are, ultimately, not comparable through bibliometrics; and highlight the benefits of telescope bibliographies, both for researchers within the astronomical community and for stakeholders beyond the specific observatories. There is tremendous diversity in the ways bibliographers track publications and maintain databases, due to parameters such as resources, type of observatory, historical practices, and reporting requirements to funders and outside agencies. However, there are also common sets of Best Practices.

astro-ph.IM↗

arXiv2023

Roman Early-Definition Astrophysics Survey Opportunity: Galactic Roman Infrared Plane Survey (GRIPS)

A wide-field near-infrared survey of the Galactic disk and bulge/bar(s) is supported by a large representation of the community of Galactic astronomers. The combination of sensitivity, angular resolution and large field of view make Roman uniquely able to study the crowded and highly extincted lines of sight in the Galactic plane. A ~1000 deg2 survey of the bulge and inner Galactic disk would yield an impressive dataset of ~120 billion sources and map the structure of our Galaxy. The effort would foster subsequent expansions in numerous dimensions (spatial, depth, wavelengths, epochs). Importantly, the survey would benefit from early defintion by the community, namely because the Galactic disk is a complex environment, and different science goals will require trade offs.

astro-ph.GA↗

arXiv2022

Best Practices for Data Publication in the Astronomical Literature

We present an overview of best practices for publishing data in astronomy and astrophysics journals. These recommendations are intended as a reference for authors to help prepare and publish data in a way that will better represent and support science results, enable better data sharing, improve reproducibility, and enhance the reusability of data. Observance of these guidelines will also help to streamline the extraction, preservation, integration and cross-linking of valuable data from astrophysics literature into major astronomical databases, and consequently facilitate new modes of science discovery that will better exploit the vast quantities of panchromatic and multi-dimensional data associated with the literature. We encourage authors, journal editors, referees, and publishers to implement the best practices reviewed here, as well as related recommendations from international astronomical organizations such as the International Astronomical Union (IAU) for publication of nomenclature, data, and metadata. A convenient Checklist of Recommendations for Publishing Data in the Literature is included for authors to consult before the submission of the final version of their journal articles and associated data files. We recommend that publishers of journals in astronomy and astrophysics incorporate a link to this document in their Instructions to Authors.

astro-ph.IM↗

arXiv2022

Spitzer Publication Statistics

We present statistics on the number of refereed astronomy journal articles that used data from NASA's Spitzer Space Telescope through the end of the calendar year 2020. We discuss the various types of science programs and science categories that were used to collect data during the mission and discuss how operational changes brought on by the depletion of cryogen in May 2009, including the resulting budget cuts, impacted the publication rate. The post-cryogenic (warm) mission produced fewer papers than the cryogenic mission, but the percentage of the exposure time published did not appreciably change between the warm and cryogenic missions. This was mostly because in the warm mission the length of observations increased, so that each warm paper on average uses more data than the cryogenic papers. We also discuss the speed of publication, archival usage, and the tremendous efficacy of the Legacy and Exploration Science programs (large, coherent investigations), including the value of having well-advertised enhanced data products hosted in centralized archives. We also identify the observations that have been published the largest number of times, and sort them by a variety of metrics (including program type, instrument used, and observation length). Data that have the highest reuse rates in publications were taken early in the Spitzer mission, or belong to one of the large surveys (large either in number of objects, in number of hours observed, or in area covered on the sky). We also assess how often authors have cited the Spitzer fundamental papers or have correctly referenced the Spitzer data they used, finding that as many as 40% of papers have failed to cite the papers, and 15% have made it impossible to identify the data they used.

astro-ph.IM↗

arXiv2022

The Rate, Amplitude and Duration of Outbursts from Class 0 Protostars in Orion

At least half of a protostar's mass is accreted in the Class 0 phase, when the central protostar is deeply embedded in a dense, infalling envelope. We present the first systematic search for outbursts from Class 0 protostars in the Orion clouds. Using photometry from Spitzer/IRAC spanning 2004 to 2017, we detect three outbursts from Class 0 protostars with $\ge 2$ mag changes at 3.6 or 4.5 $μ$m. This is comparable to the magnitude change of a known protostellar FU Ori outburst. Two are newly detected bursts from the protostars HOPS 12 and 124. The number of detections implies that Class 0 protostars burst every 438 yr, with a 95% confidence interval of 161 to 1884 yr. Combining Spitzer and WISE/NEOWISE data spanning 2004-2019, we show that the bursts persist for more than nine years with significant variability during each burst. Finally, we use $19-100$ $μ$m photometry from SOFIA, Spitzer and Herschel to measure the amplitudes of the bursts. Based on the burst interval, a duration of 15 yr, and the range of observed amplitudes, 3-100% of the mass accretion during the Class 0 phase occurs during bursts. In total, we show that bursts from Class 0 protostars are as frequent, or even more frequent, than those from more evolved protostars. This is consistent with bursts being driven by instabilities in disks triggered by rapid mass infall. Furthermore, we find that bursts may be a significant, if not dominant, mode of mass accretion during the Class 0 phase.

astro-ph.SR↗

arXiv2021

Beyond the dips of V807 Tau, a spectropolarimetric study of a dipper s magnetosphere

We aim to characterize the magnetospheric accretion process in the young stellar object V807 Tau, one of the most stable dippers revealed by K2 in the Taurus star forming region. We performed photometric and spectropolarimetric follow-up observations of this system with CFHT/ESPaDOnS in order to investigate its variability over several rotational periods. We derive a 4.38 day period from the K2 light curve. This period is also seen in the radial velocity variations, ascribed to spot modulation. The narrow component of the He I 5876 Å line as well as the red wing of the Hβ and Hγ line profiles also vary in intensity with the same periodicity. The former traces the accretion shock at the stellar surface, and the latter is a signature of an accretion funnel flow crossing the line of sight. We derive a surface brightness and magnetic field topology from the modeling of Stokes I and V profiles, respectively, for photospheric lines and for the He I line. This reveals a bright spot at the stellar surface, located at a latitude of 60 deg, and a maximum field strength of about 2 kG. The magnetic field topology at the stellar surface is dominated by a dipolar component inclined by about 40 deg onto the spin axis. Despite of its clear and stable dipper behavior, we derive a relatively low inclination of about 50 deg for this system, which calls question the origin of the dips. This low inclination is also consistent with the absence of deep inverse P Cygni components in the line profiles. We conclude that magnetospheric accretion is ongoing in V807 Tau, taking place through non-axisymmetric accretion funnel flows controlled by a strong, tilted, and mainly dipolar magnetic topology. Whether an inner disk warp resulting from this process can account for the dipper character of this source remains to be seen, given the low inclination of the system.

astro-ph.SR↗

arXiv2020

An Asymmetric Eclipse Seen Towards the Pre-Main Sequence Binary System V928 Tau

K2 observations of the weak-lined T Tauri binary V928 Tau A+B show the detection of a single, asymmetric eclipse which may be due to a previously unknown substellar companion eclipsing one component of the binary with an orbital period $>$ 66 days. Over an interval of about 9 hours, one component of the binary dims by around 60%, returning to its normal brightness about 5 hours later. From modeling of the eclipse shape we find evidence that the eclipsing companion may be surrounded by a disk or a vast ring system. The modeled disk has a radius of $0.9923\,\pm\,0.0005\,R_*$, with an inclination of $56.78\,\pm\, 0.03^\circ$, a tilt of $41.22\,\pm\,0.05^\circ$, an impact parameter of $-0.2506\,\pm\,0.0002\,R_*$ and an opacity of 1.00. The occulting disk must also move at a transverse velocity of $6.637\,\pm\,0.002\,R_*\,\mathrm{day}^{-1}$, which depending on whether it orbits V928 Tau A or B, corresponds to approximately 73.53 or 69.26 $\mathrm{km s}^{-1}$. A search in ground based archival data reveals additional dimming events, some of which suggest periodicity, but no unambiguous period associated with the eclipse observed by K2. We present a new epoch of astrometry which is used to further refine the orbit of the binary, presenting a new lower bound of 67 years, and constraints on the possible orbital periods of the eclipsing companion. The binary is also separated by 18" ($\sim$2250 au) from the lower mass CFHT-BD-Tau 7, which is likely associated with V928 Tau A+B. We also present new high dispersion optical spectroscopy that we use to characterize the unresolved stellar binary.

astro-ph.SR↗

arXiv2020

Pleiades or Not? Resolving the Status of the Lithium Rich M Dwarfs HHJ339 and HHJ430

Oppenheimer et al. (1997) discovered two M5 dwarfs in the Pleiades with nearly primordial lithium. These stars are not low enough in mass to represent the leading edge of the lithium depletion boundary at Pleiades age (~125 Myr). A possible explanation for the enhanced lithium in these stars is that they are actually not members of the Pleiades but instead are members of a younger moving group seen in projection towards the Pleiades. We have used data from Gaia DR2 to confirm that these two stars, HHJ 339 and HHJ 430, are indeed not members of the Pleiades. Based on their space motions, parallaxes and positions in a Gaia-based CMD, it is probable that these two stars are about 40 parsecs foreground to the Pleiades and have ages of ~25 Myr. Kinematically they are best matched to the 32 Ori moving group.

astro-ph.SR↗

arXiv2020

Mon-735: A new low-mass pre-main sequence eclipsing binary in NGC 2264

We present Mon-735, a detached double-lined eclipsing binary (EB) member of the $\sim$3 Myr old NGC 2264 star forming region, detected by Spitzer. We simultaneously model the Spitzer light curves, follow-up Keck/HIRES radial velocities, and the system's spectral energy distribution to determine self-consistent masses, radii and effective temperatures for both stars. We find that Mon-735 comprises two pre-main sequence M dwarfs with component masses of $M = 0.2918 \pm 0.0099$ and $0.2661 \pm 0.0095$ $\rm{M}_{\odot}$, radii of $R = 0.762 \pm 0.022$ and $0.748 \pm 0.023$ $\rm{R}_{\odot}$, and effective temperatures of $T_{\rm eff} = 3260 \pm 73$ and $3213 \pm 73$ $\rm{K}$. The two stars travel on circular orbits around their common centre of mass in $P = 1.9751388 \pm 0.0000050$ days. We compare our results for Mon-735, along with another EB in NGC 2264 (CoRoT 223992193), to the predictions of five stellar evolution models. These suggest that the lower mass EB system Mon-735 is older than CoRoT 223992193 in the mass-radius diagram (MRD) and, to a lesser extent, in the Hertzsprung-Russell diagram (HRD). The MRD ages of Mon-735 and CoRoT 223992193 are $\sim$7-9 and 4-6 Myr, respectively, with the two components in each EB system possessing consistent ages.

astro-ph.SR↗

arXiv2018

The Rotational Evolution of Young, Binary M Dwarfs

We have analysed K2 light curves for more than 3,000 low mass stars in the $\sim$8 Myr old Upper Sco association, the $\sim$125 Myr age Pleiades open cluster and the $\sim$700 Myr old Hyades and Praesepe open clusters to determine stellar rotation rates. Many of these K2 targets show two distinct periods, and for the lowest mass stars in these clusters virtually all of these systems with two periods are photometric binaries. The most likely explanation is that we are detecting the rotation periods for both components of these binaries. We explore the evolution of the rotation rate in both components of photometric binaries relative to one another and to non-photometric binary stars. In Upper Sco and the Pleiades, these low mass binary stars have periods that are much shorter on average and much closer to each other than would be true if drawn at random from the M dwarf single stars. In Upper Sco, this difference correlates strongly with the presence or absence of infrared excesses due to primordial circumstellar disks -- the single star population includes many stars with disks, and their rotation periods are distinctively longer on average than their binary star cousins of the same mass. By Praesepe age, the significance of the difference in rotation rate between the single and binary low mass dMs is much less, suggesting that angular momentum loss from winds for fully-convective zero-age main sequence stars erases memory of the rotation rate dichotomy for binary and single very low mass stars at later ages.

astro-ph.SR↗

arXiv2017

More Rapidly Rotating PMS M Dwarfs with Light Curves Suggestive of Orbiting Clouds of Material

In a previous paper, using data from K2 Campaign 2, we identified 11 very low mass members of the $ρ$ Oph and Upper Scorpius star-forming region as having periodic photometric variability and phased light curves showing multiple scallops or undulations. All the stars with the "scallop-shell" light curve morphology are mid-to-late M dwarfs without evidence of active accretion, and with photometric periods generally $<$1 day. Their phased light curves have too much structure to be attributed to non-axisymmetrically distributed photospheric spots and rotational modulation. We have now identified an additional eight probable members of the same star-forming region plus three stars in the Taurus star-forming region with this same light curve morphology and sharing the same period and spectral type range as the previous group. We describe the light curves of these new stars in detail and present their general physical characteristics. We also examine the properties of the overall set of stars in order to identify common features that might help elucidate the causes of their photometric variability.

astro-ph.SR↗

arXiv2017

M Dwarf rotation from the ${\it K2}$ young clusters to the field. I. A Mass-Rotation Correlation at 10 Myr

Recent observations of the low-mass rotation distributions of the Pleiades and Praesepe clusters have revealed a ubiquitous correlation between mass and rotation, such that late M dwarfs rotate an order-of-magnitude faster than early M dwarfs. In this paper, we demonstrate that this mass-rotation correlation is present in the 10 Myr Upper Scorpius association, as revealed by new ${\it K2}$ rotation measurements. Using rotational evolution models we show that the low-mass ($0.1-0.6 M_{\odot}$) rotation distribution of the 125 Myr Pleiades cluster can only be produced if it hosted an equally strong mass-rotation correlation at 10 Myr. This suggests that physical processes important in the early pre-main sequence (star formation, accretion, disk-locking) are primarily responsible for the M dwarf rotation morphology, and not quirks of later angular momentum evolution. Such early mass trends must be taken into account when constructing initial conditions for future studies of stellar rotation. Finally, we show that the average M star loses $\sim 25-40$% of its angular momentum between 10 and 125 Myr, a figure accurately and generically predicted by modern solar-calibrated wind models. Their success rules out a lossless pre-main sequence, and validates the extrapolation of magnetic wind laws designed for solar-type stars to the low-mass regime at early times.

astro-ph.SR↗

arXiv2017

New low-mass eclipsing binary systems in Praesepe discovered by K2

We present the discovery of four low-mass ($M<0.6$ $M_\odot$) eclipsing binary (EB) systems in the sub-Gyr old Praesepe open cluster using Kepler/K2 time-series photometry and Keck/HIRES spectroscopy. We present a new Gaussian process eclipsing binary model, GP-EBOP, as well as a method of simultaneously determining effective temperatures and distances for EBs. Three of the reported systems (AD 3814, AD 2615 and AD 1508) are detached and double-lined, and precise solutions are presented for the first two. We determine masses and radii to 1-3% precision for AD 3814 and to 5-6% for AD 2615. Together with effective temperatures determined to $\sim$50 K precision, we test the PARSEC v1.2 and BHAC15 stellar evolution models. Our EB parameters are more consistent with the PARSEC models, primarily because the BHAC15 temperature scale is hotter than our data over the mid M-dwarf mass range probed. Both ADs 3814 and 2615, which have orbital periods of 6.0 and 11.6 days, are circularized but not synchronized. This suggests that either synchronization proceeds more slowly in fully convective stars than the theory of equilibrium tides predicts or magnetic braking is currently playing a more important role than tidal forces in the spin evolution of these binaries. The fourth system (AD 3116) comprises a brown dwarf transiting a mid M-dwarf, which is the first such system discovered in a sub-Gyr open cluster. Finally, these new discoveries increase the number of characterized EBs in sub-Gyr open clusters by 20% (40%) below $M<1.5$ $M_{\odot}$ ($M<0.6$ $M_{\odot}$).

astro-ph.SR↗

arXiv2017

Orbiting Clouds of Material at the Keplerian Co-Rotation Radius of Rapidly Rotating Low Mass WTTs in Upper Sco

Using K2 data, we have identified 23 very low mass members of the $ρ$ Oph and Upper Scorpius star-forming region as having periodic photometric variability not easily explained by well-established physical mechanisms such as star spots, eclipsing binaries, or pulsation. All of these unusual stars are mid-to-late M dwarfs without evidence of active accretion, and with photometric periods generally $<$1 day. Often the unusual light curve signature takes the form of narrow flux dips; when we also have rotation periods from star spots, the two periods agree, suggesting that the flux dips are due to material orbiting the star at the Keplerian co-rotation radius. We sometimes see "state-changes" in the phased light curve morphologies where $\sim$25% of the waveform changes shape on timescales less than a day; often, the "state-change" takes place immediately after a strong flare. For the group of stars with these sudden light curve morphology shifts, we attribute their flux dips as most probably arising from eclipses of warm coronal gas clouds, analogous to the sling-shot prominences postulated to explain transient H$α$ absorption features in AB Doradus itself and other rapidly rotating late type stars. For another group of stars with somewhat longer periods, we find the short duration flux dips to be highly variable on both short and long timescales, with generally asymmetric flux dip profiles. We believe that these flux dips are due to particulate clouds possibly associated with a close-in planet or resulting from a recent collisional event.

astro-ph.SR↗

arXiv2016

CSI 2264: Accretion process in classical T Tauri stars in the young cluster NGC 2264

Our goal is to relate the photometric and spectroscopic variability of classical T Tauri stars, of the star-forming cluster NGC 2264, to the physical processes acting in the stellar and circumstellar environment, within a few stellar radii from the star. NGC 2264 was the target of a multiwavelength observational campaign with CoRoT, MOST, Spitzer, and Chandra satellites and observations from the ground. We classified the CoRoT light curves of accreting systems according to their morphology and compared our classification to several accretion diagnostics and disk parameters. The morphology of the CoRoT light curve reflects the evolution of the accretion process and of the inner disk region. Accretion burst stars present high mass-accretion rates and optically thick inner disks. AA Tau-like systems, whose light curves are dominated by circumstellar dust obscuration, show intermediate mass-accretion rates and are located in the transition of thick to anemic disks. Classical T Tauri stars with spot-like light curves correspond mostly to systems with a low mass-accretion rate and low mid-IR excess. About 30% of the classical T Tauri stars observed in the 2008 and 2011 CoRoT runs changed their light-curve morphology. Transitions from AA Tau-like and spot-like to aperiodic light curves and vice versa were common. The analysis of the $Hα$ emission line variability of 58 accreting stars showed that 8 presented a periodicity that in a few cases was coincident with the photometric period. The blue and red wings of the $Hα$ line profiles often do not correlate with each other, indicating that they are strongly influenced by different physical processes. Accreting stars have a dynamic stellar and circumstellar environment that can be explained by magnetospheric accretion and outflow models, including variations from stable to unstable accretion regimes on timescales of a few years

astro-ph.SR↗

arXiv2016

CSI 2264: Characterizing Young Stars in NGC 2264 with Stochastically Varying Light Curves

We provide CoRoT and Spitzer light curves, as well as broad-band multi-wavelength photometry and high resolution, multi- and single-epoch spectroscopy for 17 classical T Tauris in NGC 2264 whose CoRoT light curves (LCs) exemplify the "stochastic" LC class as defined in Cody et al. (2014). The most probable physical mechanism to explain the optical variability in this LC class is time-dependent mass accretion onto the stellar photosphere, producing transient hot spots. As evidence in favor of this hypothesis, multi-epoch high resolution spectra for a subset of these stars shows that their veiling levels also vary in time and that this veiling variability is consistent in both amplitude and timescale with the optical LC morphology. Furthermore, the veiling variability is well-correlated with the strength of the HeI 6678A emission line, a feature predicted by models to arise in accretion shocks on or near the stellar photosphere. Stars with accretion burst LC morphology (Stauffer et al. 2014) are also attributed to variable mass accretion. Both the stochastic and accretion burst LCs can be explained by a simple model of randomly occurring flux bursts, with the stochastic LC class having a higher frequency of lower amplitude events. Based on their UV excesses, veiling, and mean Ha equivalent widths, members of the stochastic LC class have only moderate time-averaged mass accretion rates. The most common feature of their Ha profiles is for them to exhibit blue-shifted absorption features, most likely originating in a disk wind. The lack of periodic signatures in the LCs suggests that little of the variability is due to long-lived hot spots rotating into or out of our line of sight; instead, the primary driver of the observed photometric variability is likely to be instabilities in the inner disk that lead to variable mass accretion.

astro-ph.SR↗

arXiv2015

UV variability and accretion dynamics in the young open cluster NGC 2264

We explore UV and optical variability signatures for several hundred members of NGC 2264 (3 Myr). We performed simultaneous u- and r-band monitoring over two full weeks with CFHT/MegaCam. About 750 young stars are probed; 40% of them are accreting. Statistically distinct variability properties are observed for accreting and non-accreting cluster members. The accretors exhibit a significantly higher level of variability than the non-accretors, especially in the UV. The amount of u-band variability correlates statistically with UV excess in disk-bearing objects, which suggests that accretion and star-disk interaction are the main sources of variability. Cool magnetic spots, several hundred degrees colder than the photosphere and covering from 5 to 30% of the stellar surface, appear to be the leading factor of variability for the non-accreting stars. In contrast, accretion spots, a few thousand degrees hotter than the photosphere and covering a few percent of the stellar surface, best reproduce the variability of accreting objects. The color behavior is also found to be different between accreting and non-accreting stars. Typical variability amplitudes for accreting members rapidly increase from r to u, which indicates a much stronger contrast at short wavelengths; a lower color dependence in the amplitudes is instead measured for diskless stars. We find that u-band variability on hour timescales is typically about 10% of the peak-to-peak variability on day timescales, while longer term (years) variability is consistent with amplitudes measured over weeks. We conclude that for both accreting and non-accreting stars, the mid-term rotational modulation by spots is the leading timescale for a variability of up to several years. In turn, this suggests that the accretion process is essentially stable over years, although it exhibits low-level shorter term variations in single accretion events.

astro-ph.SR↗