arXiv subjects

L. M. Rebull

Publications and source records attributed to L. M. Rebull.

At least 19 recordsLinked to original sources

arXiv2024

Circumstellar disk accretion across the Lagoon Nebula: the influence of environment and stellar mass

Pre-main sequence disk accretion is pivotal in determining the final stellar properties and the early conditions for close-in planets. We aim to establish the impact of internal (stellar mass) and external (radiation field) parameters on disk evolution in the Lagoon Nebula massive star-forming region. We employ simultaneous $u,g,r,i,Hα$ time series photometry, archival infrared data, and high-precision $K2$ light curves, to derive stellar, disk, and accretion properties for 1012 Lagoon Nebula members. Of all young stars in the Lagoon Nebula, we estimate $34\%-37\%$ have inner disks traceable down to $\sim 12$ $μ$m, while $38\%-41\%$ are actively accreting. We detect disks $\sim$1.5 times more frequently around G/K/M stars than higher-mass stars, which appear to deplete their inner disks on shorter timescales. We find tentative evidence for faster disk evolution in the central regions of the Lagoon Nebula, where the bulk of the O/B population is located. Conversely, disks appear to last longer at its outskirts, where the measured fraction of disk-bearing stars tends to exceed those of accreting and disk-free stars. The derived mass accretion rates show a non-uniform dependence on stellar mass between $\sim 0.2-5$ $M_\odot$. In addition, the typical accretion rates appear to differ across the Lagoon Nebula extension, with values two times lower in the core region than at its periphery. Finally, we detect tentative density gradients in the accretion shocks, with lags in the appearance of brightness features as a function of wavelength that can amount to $\sim7\%-30\%$ of the rotation period.

astro-ph.SR↗

arXiv2023

Young Stellar Object Candidates in IC 417

IC 417 is in the Galactic Plane, and likely part of the Aur OB2 association; it is ~2 kpc away. Stock 8 is one of the densest cluster constituents; off of it to the East, there is a 'Nebulous Stream' (NS) that is dramatic in the infrared (IR). We have assembled a list of literature-identified young stellar objects (YSOs), new candidate YSOs from the NS, and new candidate YSOs from IR excesses. We vetted this list via inspection of the images, spectral energy distributions (SEDs), and color-color/color-magnitude diagrams. We placed the 710 surviving YSOs and candidate YSOs in ranked bins, nearly two-thirds of which have more than 20 points defining their SEDs. The lowest-ranked bins include stars that are confused, or likely carbon stars. There are 503 in the higher-ranked bins; half are SED Class III, and $\sim$40\% are SED Class II. Our results agree with the literature in that we find that the NS and Stock 8 are at about the same distance as each other (and as the rest of the YSOs), and that the NS is the youngest region, with Stock 8 a little older. We do not find any evidence for an age spread within the NS, consistent with the idea that the star formation trigger came from the north. We do not find that the other literature-identified clusters here are as young as either the NS or Stock 8; at best they are older than Stock 8, and they may not all be legitimate clusters.

astro-ph.SR↗

arXiv2023

Stable accretion and episodic outflows in the young transition disk system GM Aurigae

We investigate the structure and dynamics of the magnetospheric accretion region and associated outflows on a scale smaller than 0.1 au around the young transitional disk system GM Aur. We monitored the variability of the system on timescales ranging from days to months, using high-resolution optical and near-infrared spectroscopy, multiwavelength photometry, and low-resolution near-infrared spectroscopy, over a total duration of six months (30 rotational cycles). We analyzed the photometric and line profile variability to characterize the accretion and ejection processes. The luminosity of the system is modulated by surface spots at the stellar rotation period of 6.04 days. The Balmer, Paschen, and Brackett hydrogen lines as well as the HeI 5876 A and HeI 10830 A line profiles are modulated on the same period. The PaB line flux correlates with the photometric excess in the u' band, which suggests that most of the line emission originates from the accretion process. High-velocity redshifted absorptions reaching below the continuum periodically appear in the near-infrared line profiles at the rotational phase in which the veiling and line fluxes are the largest. These are signatures of a stable accretion funnel flow and associated accretion shock at the stellar surface. This large-scale magnetospheric accretion structure appears fairly stable over at least 15 and possibly up to 30 rotational periods. In contrast, outflow signatures randomly appear as blueshifted absorption components in the Balmer and HeI 10830 A line profiles and disappear on a timescale of a few days. The coexistence of a stable, large-scale accretion pattern and episodic outflows supports magnetospheric ejections as the main process occurring at the star-disk interface. Stable magnetospheric accretion and episodic outflows appear to be physically linked on a scale of a few stellar radii in this system.

astro-ph.SR↗

arXiv2022

Rotation of Low-Mass Stars in Upper Centaurus Lupus and Lower Centaurus Crux with TESS

We present stellar rotation rates derived from Transiting Exoplanet Survey Satellite (TESS) light curves for stars in Upper Centaurus-Lupus (UCL; ~136 pc, ~16 Myr) and Lower Centaurus-Crux (LCC; ~115 pc, ~17 Myr). We find spot-modulated periods (P) for ~90% of members. The range of light curve and periodogram shapes echoes that found for other clusters with K2, but fewer multi-period stars may be an indication of different noise characteristics of TESS, or a result of the source selection methods here. The distribution of P as a function of color as a proxy for mass fits nicely in between that for both older and younger clusters observed by K2, with fast rotators found among both the highest and lowest masses probed here, and a well-organized distribution of M star rotation rates. About 13% of the stars have an infrared (IR) excess, suggesting a circumstellar disk; this is well-matched to expectations, given the age of the stars. There is an obvious pile-up of disked M stars at P~2 days, and the pile-up may move to shorter P as the mass decreases. There is also a strong concentration of disk-free M stars at P~2 days, hinting that perhaps these stars have recently freed themselves from their disks. Exploring the rotation rates of stars in UCL/LCC has the potential to help us understand the beginning of the end of the influence of disks on rotation, and the timescale on which the star responds to unlocking.

astro-ph.SR↗

arXiv2020

Even More Rapidly Rotating Pre-Main Sequence M Dwarfs with Highly Structured Light Curves: An Initial Survey in the Lower Centaurus-Crux and Upper Centaurus-Lupus Associations

Using K2, we recently discovered a new type of periodic photometric variability while analysing the light curves of members of Upper Sco (Stauffer \etal\ 2017). The 23 exemplars of this new variability type are all mid-M dwarfs, with short rotation periods. Their phased light curves have one or more broad flux dips or multiple arcuate structures which are not explicable by photospheric spots or eclipses by solid bodies. Now, using TESS data, we have searched for this type of variability in the other major sections of Sco-Cen, Upper Centaurus-Lupus (UCL) and Lower Centaurus-Crux (LCC). We identify 28 stars with the same light curve morphologies. We find no obvious difference between the Upper Sco and the UCL/LCC representatives of this class in terms of their light curve morphologies, periods or variability amplitudes. The physical mechanism behind this variability is unknown, but as a possible clue we show that the rapidly rotating mid-M dwarfs in UCL/LCC have slightly different colors from the slowly rotating M dwarfs - they either have a blue excess (hot spots?) or a red excess (warm dust?). One of the newly identified stars (TIC242407571) has a very striking light curve morphology. At about every 0.05 in phase are features that resemble icicles, The "icicles" arise because there is a second periodic system whose main feature is a broad flux dip. Using a toy model, we show that the observed light curve morphology results only if the ratio of the two periods and the flux dip width are carefully arranged.

astro-ph.SR↗

arXiv2020

Investigating the magnetospheric accretion process in the young pre-transitional disk system DoAr 44 (V2062~Oph). A multiwavelength interferometric, spectropolarimetric, and photometric observing campaign

Young stars interact with their accretion disk through their strong magnetosphere. We investigate the magnetospheric accretion process in the young stellar system DoAr 44. We monitored the system over several rotational cycles, combining high-resolution optical and near-IR spectropolarimetry with long-baseline near-IR interferometry and multicolor photometry. DoAr 44 is a young 1.2 solar mass star, moderately accreting from its disk, and seen at a low inclination. We derive a rotational period of 2.96 d from the system's light curve. Several optical and near-IR line profiles probing the accretion funnel flows and the accretion shock are modulated at the stellar rotation period. The most variable line profile, HeI 1083 nm, exhibits modulated redshifted wings a signature of accretion funnel flows, as well as deep blueshifted absorptions indicative of transient outflows. The Zeeman-Doppler analysis suggests the star hosts a mainly dipolar magnetic field, inclined by about 20 deg. onto the spin axis, with an intensity reaching about 800 G at the photosphere, and up to 2 +/- 0.8 kG close to the accretion shock. The magnetic field appears strong enough to disrupt the inner disk close to the corotation radius, at a distance of about 4.6 stellar radii (0.043 au). This supports the upper limit of 5 stellar radii (0.047 au) we derived for the size of the magnetosphere from long baseline interferometry. DoAr 44 is a pre-transitional disk system, exhibiting a 25-30 au gap in its circumstellar disk, with the inner and outer disks being misaligned. On a scale of 0.1 au or less, our results indicate that the system steadily accretes from its inner disk through its tilted dipolar magnetosphere. We conclude that in spite of a highly structured outer disk, perhaps the signature of ongoing planetary formation, the magnetospheric accretion process proceeds unimpeded at the star-disk interaction level.

astro-ph.SR↗

arXiv2020

Rotation of Low-Mass Stars in Taurus with K2

We present an analysis of K2 light curves (LCs) from Campaigns 4 and 13 for members of the young ($\sim$3 Myr) Taurus association, in addition to an older ($\sim$30 Myr) population of stars that is largely in the foreground of the Taurus molecular clouds. Out of 156 of the highest-confidence Taurus members, we find that 81\% are periodic. Our sample of young foreground stars is biased and incomplete, but nearly all (37/38) are periodic. The overall distribution of rotation rates as a function of color (a proxy for mass) is similar to that found in other clusters: the slowest rotators are among the early M spectral types, with faster rotation towards both earlier FGK and later M types. The relationship between period and color/mass exhibited by older clusters such as the Pleiades is already in place by Taurus age. The foreground population has very few stars, but is consistent with the USco and Pleiades period distributions. As found in other young clusters, stars with disks rotate on average slower, and few with disks are found rotating faster than $\sim$2 d. The overall amplitude of the light curves decreases with age and higher mass stars have generally lower amplitudes than lower mass stars. Stars with disks have on average larger amplitudes than stars without disks, though the physical mechanisms driving the variability and the resulting light curve morphologies are also different between these two classes.

astro-ph.SR↗

arXiv2019

Near-Infrared Variability of Low Mass Stars in IC 1396A and TR 37

We have monitored nearly a square degree in IC 1396A/Tr 37 over 21 epochs extending over 2014 - 2016 for sources variable in the JHK bands. In our data, 65 +\- 8 % of previously identified cluster members show variations, compared with < 0.3% of field stars. We identify 119 members of Tr 37 on the basis of variability, forming an unbiased sample down to the brown dwarf regime. The K-band luminosity function in Tr 37 is similar to that of IC 348 but shifted to somewhat brighter values, implying that the K- and M-type members of Tr 37 are younger than those in IC 348. We introduce methods to classify the causes of variability, based on behavior in the color-color and color-magnitude diagrams. Accretion hot spots cause larger variations at J than at K with substantial scatter in the diagrams; there are at least a dozen, with the most active resembling EXors. Eleven sources are probably dominated by intervention of dust clumps in their circumstellar disks with color behavior indicating the presence of grains larger than for interstellar dust, presumably due to grain growth in their disks. Thirteen sources have larger variations at K than at J or H. For 11 of them, the temperature fitted to the variable component is very close to 2000K, suggesting that the changes in output are caused by turbulence at the inner rim of the circumstellar disk exposing previously protected populations of grains.

astro-ph.SR↗

arXiv2019

Simultaneous Kepler/K2 and XMM-Netwon observations of superflares in the Pleiades

Flares are powerful events ignited by a sudden release of magnetic energy. With the aim of studying flares in the 125-Myr-old stars in the Pleiades observed simultaneously in optical and X-ray light, we obtained new XMM-Newton observations of this cluster during the observations of Kepler K2 Campaign 4. Our objective is to characterize the most powerful flares observed in both bands and to constrain the energy released in the optical and X-ray, the geometry of the loops, and their time evolution. We aim to compare our results to existing studies of flares occurring in the Sun and stars at different ages. We selected bright X-ray/optical flares occurred in 12 known members of the Pleiades from their K2 and XMM-Newton light curves. The sample includes ten K-M stars, one F9 star, and one G8 star. Flare average properties were obtained from integrated analysis of the light curves during the flares. The time evolution of the plasma in the magnetic loops is constrained with time-resolved X-ray spectral analysis. Most of the flares studied in this work emitted more energy in optical than in X-rays, as in most solar flares, even if the Pleiades flares output a larger fraction of their total energy in X-rays than typical solar flares do. Additionally, the energy budget in the two bands is weakly correlated. We also found comparable flare duration in optical and X-rays and observed that rapidly rotating stars (e.g., with rotation period shorter than 0.5 days) preferentially host short flares. We estimated the slope of the cooling path of the flares in the log(EM)-versus-log(T) plane. The values we obtained are affected by large uncertainties, but their nominal values suggest that the flares analyzed in this paper are mainly due to single loops with no sustained heating occurring during the cooling phase. We also observed and analyzed oscillations with a period of 500 s during one of the flares.

astro-ph.SR↗

arXiv2018

Major Outcomes of an Authentic Astronomy Research Experience Professional Development Program: An Analysis of 8 Years of Data from NITARP

The NASA/IPAC Teacher Archive Research Program (NITARP) provides a year-long authentic astronomy research project by partnering a research astronomer with small groups of educators. NITARP has worked with a total of 103 educators since 2005. In this paper, surveys are explored that were obtained from 74 different educators, at up to four waypoints during the course of 13 months, from the class of 2010 through the class of 2017; those surveys reveal how educator participants describe the major changes and outcomes in themselves fostered by NITARP. Three-quarters of the educators self-report some or major changes in their understanding of the nature of science. The program provides educators with experience collaborating with astronomers and other educators, and forges a strong link to the astronomical research community; the NITARP community of practice encourages and reinforces these linkages. During the experience, educators get comfortable with learning complex new concepts, with ~40% noting in their surveys that their approach to learning has changed. Educators are provided opportunities for professional growth; at least 12% have changed career paths substantially in part due to the program, and 14\% report that the experience was "life changing." At least 60% express a desire to include richer, more authentic science activities in their classrooms. This work illuminates what benefits the program brings to its participants; the NITARP approach could be mirrored in similar professional development (PD) programs in other STEM subjects.

physics.ed-ph↗

arXiv2018

Motivations of Educators for Participating in NITARP, an Authentic Astronomy Research Experience Professional Development Program

The NASA/IPAC Teacher Archive Research Program (NITARP) partners small groups of educators with a research astronomer for a year-long authentic research project. This program aligns well with the characteristics of high-quality professional development (PD) programs and has worked with a total of 103 educators since 2005. In this paper, surveys were explored that were obtained from 74 different educators, at up to four waypoints during the course of 13 months, incorporating data from the class of 2010 through the class of 2017. This paper investigates how participating teachers describe their motivations for participating in NITARP as evidenced in these feedback forms. Analysis of self-reported data allows a mapping onto a continuum ranging from more inward-focused to more outward-focused; there is a shift from more inward-focused responses to more outward-focused responses. This insight into teacher motivations has implications for how the educators might be supported during their year with the program. This work provides a new way of parameterizing why educators participate in PD programs that require a considerable investment of time. NITARP, since it has many qualities of successful PD, serves as a model for similar PD programs in other STEM subjects. Likewise, the analysis method might also be useful to similarly evaluate other PD programs.

physics.ed-ph↗

arXiv2018

Authentic Research in the Classroom for Teachers and Students

With the advent of research-grade robotic telescopes (and professional archives) coupled with the wide availability of the Internet in schools, getting high-quality data in the classroom has become much easier than ever before. Robotic telescopes (and archives) have revolutionized what is possible to accomplish in the confines of a high school classroom. Especially in the context of new science standards in the US, schools need to be moving towards more project-based learning and incorporating more authentic scientific inquiry, so demand for programs such as this is only expected to grow. This contribution highlights a few of the programs that incorporate authentic research in the classroom, via teachers and/or students. I also point out some recurring themes among these programs and suggest a funnel as a way to think about the 'ecosystem' of projects getting astronomical data into the hands of teachers, students, and the public.

physics.ed-ph↗

arXiv2018

The NASA/IPAC Teacher Archive Research Program (NITARP)

NITARP, the NASA/IPAC Teacher Archive Research Program, partners small groups of predominantly high school educators with research astronomers for a year-long research project. This paper presents a summary of how NITARP works and the lessons learned over the last 13 years. The program lasts a calendar year, January to January, and involves three ~week-long trips: to the American Astronomical Society (AAS) winter meeting, to Caltech in the summer (with students), and back to a winter AAS meeting (with students) to present their results. Because NITARP has been running since 2009, and its predecessor ran from 2005-2008, there have been many lessons learned over the last 13 years that have informed the development of the program. The most critical is that scientists must see their work with the educators on their team as a partnership of equals who have specialized in different professions. NITARP teams appear to function most efficiently with approximately 5 people: a mentor astronomer, a mentor teacher (who has been through the program before), and 3 new educators. Educators are asked to step into the role of learner and develop their question-asking skills as they work to develop an understanding of a subject in which they will not have command of all the information and processes needed. Critical to the success of each team is the development of communication skills and fluid plan of action to keep the lines of communication open. This program has allowed more than 100 educators to present more than 60 total science posters at the AAS.

physics.ed-ph↗

arXiv2018

Rotation of Low-Mass Stars in Upper Scorpius and Rho Ophiuchus with K2

We present an analysis of K2 light curves (LCs) for candidate members of the young Upper Sco (USco) association $\sim$8 Myr) and the neighboring Rho Oph embedded cluster ($\sim$1 Myr). We establish $\sim$1300 stars as probable members, $\sim$80\% of which are periodic. The phased LCs have a variety of shapes which can be attributed to physical causes ranging from stellar pulsation and stellar rotation to disk-related phenomena. We identify and discuss a number of observed behaviors. The periods are $\sim$0.2-30 days with a peak near 2 days and the rapid period end nearing break-up velocity. M stars in the young USco region rotate systematically faster than GK stars, a pattern also present in K2 data for the older Pleiades and Praesepe systems. At higher masses (types FGK), the well-defined period-color relationship for slowly rotating stars seen in the Pleiades and Praesepe is not yet present in USco. Circumstellar disks are present predominantly among the more slowly rotating Ms in USco, with few disks in the sub-day rotators. However, M dwarfs with disks rotate faster on average than FGK systems with disks. For four of these disked Ms, we provide direct evidence for disk-locking based on the K2 LC morphologies. Our preliminary analysis shows a relatively mass-independent spin-up by a factor of $\sim$3.5 between USco and the Pleiades, then mass-dependent spin-down between Pleiades and Praesepe.

astro-ph.SR↗

arXiv2017

NASA's Long-Term Astrophysics Data Archives

NASA regards data handling and archiving as an integral part of space missions, and has a strong track record of serving astrophysics data to the public, beginning with the the IRAS satellite in 1983. Archives enable a major science return on the significant investment required to develop a space mission. In fact, the presence and accessibility of an archive can more than double the number of papers resulting from the data. In order for the community to be able to use the data, they have to be able to find the data (ease of access) and interpret the data (ease of use). Funding of archival research (e.g., the ADAP program) is also important not only for making scientific progress, but also for encouraging authors to deliver data products back to the archives to be used in future studies. NASA has also enabled a robust system that can be maintained over the long term, through technical innovation and careful attention to resource allocation. This article provides a brief overview of some of NASA's major astrophysics archive systems, including IRSA, MAST, HEASARC, KOA, NED, the Exoplanet Archive, and ADS.

astro-ph.IM↗

arXiv2017

Rotation of Late-Type Stars in Praesepe with K2

We have Fourier analyzed 941 K2 light curves of likely members of Praesepe, measuring periods for 86% and increasing the number of rotation periods (P) by nearly a factor of four. The distribution of P vs. (V-K), a mass proxy, has three different regimes: (V-K)<1.3, where the rotation rate rapidly slows as mass decreases; 1.3<(V-K)<4.5, where the rotation rate slows more gradually as mass decreases; and (V-K)>4.5, where the rotation rate rapidly increases as mass decreases. In this last regime, there is a bimodal distribution of periods, with few between $\sim$2 and $\sim$10 days. We interpret this to mean that once M stars start to slow down, they do so rapidly. The K2 period-color distribution in Praesepe ($\sim$790 Myr) is much different than in the Pleiades ($\sim$125 Myr) for late F, G, K, and early-M stars; the overall distribution moves to longer periods, and is better described by 2 line segments. For mid-M stars, the relationship has similarly broad scatter, and is steeper in Praesepe. The diversity of lightcurves and of periodogram types is similar in the two clusters; about a quarter of the periodic stars in both clusters have multiple significant periods. Multi-periodic stars dominate among the higher masses, starting at a bluer color in Praesepe ((V-K)$\sim$1.5) than in the Pleiades ((V-K)$\sim$2.6). In Praesepe, there are relatively more light curves that have two widely separated periods, $ΔP >$6 days. Some of these could be examples of M star binaries where one star has spun down but the other has not.

astro-ph.SR↗

arXiv2016

CSI 2264: Investigating rotation and its connection with disk accretion in the young open cluster NGC 2264

The low spin rates measured for solar-type stars at an age of a few Myr (~10% of the break-up velocity) indicate that some mechanism of angular momentum regulation must be at play in the early pre-main sequence. We characterize the rotation properties for members of the region NGC 2264 (~3 Myr), and investigate the accretion-rotation connection at an age where about 50% of the stars have already lost their disks. We examined a sample of 500 cluster members whose photometric variations were monitored in the optical for 38 consecutive days with CoRoT. Light curves were analyzed for periodicity using the Lomb-Scargle periodogram, the autocorrelation function and the string-length method. The period distribution obtained for the cluster consists of a smooth distribution centered around P=5.2 d with two peaks at P=1-2 d and 3-4 d. A separate analysis of CTTS and WTTS indicates that the P=1-2 d peak is associated with the latter, while both groups contribute to the P=3-4 d peak. The comparison between CTTS and WTTS supports the idea of a rotation-accretion connection: their respective rotational properties are statistically different, and CTTS rotate on average more slowly than WTTS. We also observe a clear dearth of fast rotators with strong accretion signatures (large UV flux excess). This is consistent with earlier findings that fast rotators in young star clusters are typically devoid of dusty disks. Our sample shows some evidence of a mass dependence in the rotation properties of NGC 2264 members, lower-mass stars spinning on average faster. This study confirms that disks influence the rotational evolution of young stars. The idea of disk-locking may be consistent with the picture of rotation and rotation-accretion connection that we observe for the NGC 2264 cluster. However, the origin of the several substructures that we observe in the period distribution deserves further investigation.

astro-ph.SR↗

arXiv2016

Spitzer Space Telescope Mid-IR Light Curves of Neptune

We have used the Spitzer Space Telescope in February 2016 to obtain high cadence, high signal-to-noise, 17-hour duration light curves of Neptune at 3.6 and 4.5 $μ$m. The light curve duration was chosen to correspond to the rotation period of Neptune. Both light curves are slowly varying with time, with full amplitudes of 1.1 mag at 3.6 $μ$m and 0.6 mag at 4.5 $μ$m. We have also extracted sparsely sampled 18-hour light curves of Neptune at W1 (3.4 $μ$m) and W2 (4.6 $μ$m) from the WISE/NEOWISE archive at six epochs in 2010-2015. These light curves all show similar shapes and amplitudes compared to the Spitzer light curves but with considerable variation from epoch to epoch. These amplitudes are much larger than those observed with Kepler/K2 in the visible (amplitude $\sim$0.02 mag) or at 845 nm with the Hubble Space Telescope in 2015 and at 763 nm in 2016 (amplitude $\sim$ 0.2 mag). We interpret the Spitzer and WISE light curves as arising entirely from reflected solar photons, from higher levels in Neptune's atmosphere than for K2. Methane gas is the dominant opacity source in Neptune's atmosphere, and methane absorption bands are present in the HST 763, and 845 nm, WISE W1, and Spitzer 3.6 $μ$m filters.

astro-ph.EP↗