The orbital motion of the Arches cluster — clues on cluster formation near the galactic center

The Arches cluster is one of the most massive, young clusters in the Milky Way. Located inside the central molecular zone in the inner 200 pc of the Galactic center, it formed in one of the most extreme star-forming environments in the present-day Galaxy. Its young age of only 2.5 Myr allows us to observe the cluster despite the strong tidal shear forces in the inner Galaxy. The orbit of the cluster determines its dynamical evolution, tidal stripping, and hence its fate. We have measured the proper motion of the Arches cluster relative to the ambient field from Keck/NIRC2 LGS-AO and VLT/NAOS-CONICA NGS-AO observations taken 4.3 years earlier. When combined with the radial velocity, we derive a 3D space motion of 232 ± 30 km/s for the Arches. This motion is exceptionally large when compared to molecular cloud orbits in the GC, and places stringent constraints on the formation scenarios for starburst clusters in dense, nuclear environments

Brain-Computer Interface meets ROS: A robotic approach to mentally drive telepresence robots

This paper shows and evaluates a novel approach to integrate a non-invasive Brain-Computer Interface (BCI) with the Robot Operating System (ROS) to mentally drive a telepresence robot. Controlling a mobile device by using human brain signals might improve the quality of life of people suffering from severe physical disabilities or elderly people who cannot move anymore. Thus, the BCI user is able to actively interact with relatives and friends located in different rooms thanks to a video streaming connection to the robot. To facilitate the control of the robot via BCI, we explore new ROS-based algorithms for navigation and obstacle avoidance, making the system safer and more reliable. In this regard, the robot can exploit two maps of the environment, one for localization and one for navigation, and both can be used also by the BCI user to watch the position of the robot while it is moving. As demonstrated by the experimental results, the user's cognitive workload is reduced, decreasing the number of commands necessary to complete the task and helping him/her to keep attention for longer periods of time.Comment: Accepted in the Proceedings of the 2018 IEEE International Conference on Robotics and Automatio

Doctor of Philosophy

dissertationThe hippocampus (HPP) plays an important role in episodic memory, or memory for an event that occurs in a specific place and time, and there is evidence to suggest that the HPP is involved in processing spatiotemporal information in order to form context;ual representations of memory events. The HPP is not a homogeneous structure, but instead is comprised of anatomically distinct subregions, including the dentate gyrus (DG), CA3, and CA1, associated with separate mnemonic processing functions that contribute to episodic memory formation. Specifically, the DG is thought to support spatial processing functions, whereas the CA1 subregion has been implicated in temporal processing. Despite considerable advances in our understanding of the unique contributions of HPP subregions to learning and memory processes, the role of the dorsal DG (dDG) in spatial processing as it relates to spatial representations is not entirely understood or agreed upon. Given the importance of spatial representations to spatial navigation and episodic memory function, the current investigation sought to further define the role of the dDG in spatial processing through a series of studies that explored the nature of spatial memory representations. The results suggest that the dDG plays a critical role in (1) the integration of multimodal information into unique representations of the spatial environment via conjunctive encoding, (2) the reduction of interference among similar spatial locations via spatial pattern separation, and (3) the formation of temporal associations among distinct spatial events via temporal integration. Taken together, the present findings provide evidence for a dynamic role for the dDG in spatial processing by demonstrating the importance of an intact dDG across a variety of spatial tasks and under a variety of learning and memory demands

The effect of literature mapping of basal vocabulary on word knowledge and comprehension

The purpose of this study was to ascertain whether two instructional interventions in reading that utilize literature mapping within a story element frame, T-CaPS MaP via transparency mapping, or computer-designed mapping via Inspiration, would affect reading ability of leveled sixth grade groups. T-CaPS MaP, designed by the researcher, is a combination of well-known story grammars that was used to expand and enhance basal vocabulary instruction. T represents the title of the story, C represents characters in the story; arepresents and; P represents point of view of the author; S represents setting of the story; M represents the mood of the story; arepresents and; and P represents plot/theme. Fifth grade scores on the Iowa Test of Basic Skills (ITBS ) were used to determine a high group, at or above the 60 th percentile, and a low group, at or below the 40th percentile. A quasi-experimental design utilizing the nonequivalent control-group design was used with six individual ANCOVAs to compare group mean test scores with the high and low groups among the three treatments: traditional, transparency, and Inspiration. Three schools with similar characteristics were randomly assigned to experimental and control conditions using the randomized, pretest-posttest control group design. The control school used traditional instruction as defined by the instructional practices of the classroom teacher. Six individual analyses of covariance were used to compare the three groups using pretest scores as a statistical means to remove preexisting academic elements. The level of statistical significance was set at p \u3c .05. Five of the six ANCOVAS showed that Reading Level had a significant main effect on the dependent variable scores. A relationship between reading levels and methods of instruction was determined using student scores on the Gates-MacGinitie Reading Test, used to evaluate general vocabulary and comprehension, and the Harcourt Reading Skills Assessment, used to evaluate specific vocabulary and comprehension taught from the Harcourt Reading Series. The critical comparison was between the experimental and control groups on pretests and posttests evaluating the dependent variables of vocabulary and reading comprehension. There was one interaction effect with the instructional method of Inspiration, a computer software program that produces semantic maps, between the high and low groups measuring general comprehension skills on the Gates MacGinitie Reading Test. Students in the high group, those with scores at or above the 60th percentile, scored higher on the general comprehension posttest than the other tests, and students in the low group, those with scores at or below the 40th percentile, scored lower on the general comprehension posttest than the other tests. This unexpected interaction could imply that classroom teachers should be aware of the effect of various teaching styles in the area of reading and their impact on student achievement

Nitric oxide as a putative retinal axon pathfinding and target recognition cue in Xenopus laevis

Nitric oxide (NO) is an atypical neurotransmitter synthesized by the enzyme nitric oxide synthase (NOS) during many stages of the Xenopus laevis life cycle. This research investigates whether the gas NO is involved in axon guidance, the neurodevelopmental process in which axons travel through the brain to their appropriate target locations to form functional neural circuitry. Through immunocytochemistry and direct labeling of the NO gas with a fluorescent dye, we have found that NOS expression corresponds spatiotemporally with the beginning of retinal axon innervation of the optic tectum in X. laevis. Our function-blocking studies in which NO is chemically inhibited suggest that NO may be necessary for correct pathfinding and targeting, evidenced by qualitative widening of the optic tract and aberrant target innervation

The orbital motion of the Quintuplet cluster - a common origin for the Arches and Quintuplet clusters?

We investigate the orbital motion of the Quintuplet cluster near the Galactic center with the aim of constraining formation scenarios of young, massive star clusters in nuclear environments. Three epochs of adaptive optics high-angular resolution imaging with Keck/NIRC2 and VLT/NACO were obtained over a time baseline of 5.8 years, delivering an astrometric accuracy of 0.5-1 mas/yr. Proper motions were derived in the cluster reference frame and were used to distinguish cluster members from the majority of field stars. Fitting the cluster and field proper motion distributions with 2D gaussian models, we derive the orbital motion of the cluster for the first time. The Quintuplet is moving with a 2D velocity of 132 +/- 15 km/s with respect to the field along the Galactic plane, which yields a 3D orbital velocity of 167 +/- 15 km/s when combined with the previously known radial velocity. From a sample of 119 stars measured in three epochs, we derive an upper limit to the velocity dispersion in the core of the Quintuplet cluster of sigma_1D < 10 km/s. Knowledge of the three velocity components of the Quintuplet allows us to model the cluster orbit in the potential of the inner Galaxy. Comparing the Quintuplet's orbit with the Arches orbit, we discuss the possibility that both clusters originated in the same area of the central molecular zone. [abridged]Comment: 40 pages, 12 figures, accepted for publication in Ap

Circumstellar discs in Galactic centre clusters: Disc-bearing B-type stars in the Quintuplet and Arches clusters

We investigate the circumstellar disc fraction as determined from L-band excess observations of the young, massive Arches and Quintuplet clusters residing in the central molecular zone of the Milky Way. The Quintuplet cluster was searched for L-band excess sources for the first time. We find a total of 26 excess sources in the Quintuplet cluster and 21 in the Arches cluster, of which 13 are new detections. With the aid of proper motion membership samples, the disc fraction of the Quintuplet cluster was derived for the first time to be 4.0 +/- 0.7%. There is no evidence for a radially varying disc fraction in this cluster. In the case of the Arches cluster, a disc fraction of 9.2 +/- 1.2% approximately out to the cluster's predicted tidal radius, r < 1.5 pc, is observed. This excess fraction is consistent with our previously found disc fraction in the cluster in the radial range 0.3 < r < 0.8 pc. In both clusters, the host star mass range covers late A- to early B-type stars, 2 < M < 15 Msun, as derived from J-band photospheric magnitudes. We discuss the unexpected finding of dusty circumstellar discs in these UV intense environments in the context of primordial disc survival and formation scenarios of secondary discs. We consider the possibility that the L-band excess sources in the Arches and Quintuplet clusters could be the high-mass counterparts to T Tauri pre-transitional discs. As such a scenario requires a long pre-transitional disc lifetime in a UV intense environment, we suggest that mass transfer discs in binary systems are a likely formation mechanism for the B-star discs observed in these starburst clusters.Comment: 47 pages, 22 figures, accepted by A&

Discovery of low-metallicity stars in the central parsec of the Milky Way

We present a metallicity analysis of 83 late-type giants within the central 1 pc of the Milky Way. K-band spectroscopy of these stars were obtained with the medium-spectral resolution integral-field spectrograph NIFS on Gemini North using laser-guide star adaptive optics. Using spectral template fitting with the MARCS synthetic spectral grid, we find that there is large variation in metallicity, with stars ranging from [M/H] $<$ -1.0 to above solar metallicity. About 6\% of the stars have [M/H] $<$ -0.5. This result is in contrast to previous observations, with smaller samples, that show stars at the Galactic center have approximately solar metallicity with only small variations. Our current measurement uncertainties are dominated by systematics in the model, especially at [M/H] $>$ 0, where there are stellar lines not represented in the model. However, the conclusion that there are low metallicity stars, as well as large variations in metallicity is robust. The metallicity may be an indicator of the origin of these stars. The low-metallicity population is consistent with that of globular clusters in the Milky Way, but their small fraction likely means that globular cluster infall is not the dominant mechanism for forming the Milky Way nuclear star cluster. The majority of stars are at or above solar metallicity, which suggests they were formed closer to the Galactic center or from the disk. In addition, our results indicate that it will be important for star formation history analyses using red giants at the Galactic center to consider the effect of varying metallicity.Comment: 11 pages, 10 figures, ApJ Accepte

Properties of the Remnant Clockwise Disk of Young Stars in the Galactic Center

We present new kinematic measurements and modeling of a sample of 116 young stars in the central parsec of the Galaxy in order to investigate the properties of the young stellar disk. The measurements were derived from a combination of speckle and laser guide star adaptive optics imaging and integral field spectroscopy from the Keck telescopes. Compared to earlier disk studies, the most important kinematic measurement improvement is in the precision of the accelerations in the plane of the sky, which have a factor of six smaller uncertainties (~10 uas/yr/yr). We have also added the first radial velocity measurements for 8 young stars, increasing the sample at the largest radii (6"-12") by 25%. We derive the ensemble properties of the observed stars using Monte-Carlo simulations of mock data. There is one highly significant kinematic feature (~20 sigma), corresponding to the well-known clockwise disk, and no significant feature is detected at the location of the previously claimed counterclockwise disk. The true disk fraction is estimated to be ~20%, a factor of ~2.5 lower than previous claims, suggesting that we may be observing the remnant of what used to be a more densely populated stellar disk. The similarity in the kinematic properties of the B stars and the O/WR stars suggests a common star formation event. The intrinsic eccentricity distribution of the disk stars is unimodal, with an average value of = 0.27 +/- 0.07, which we show can be achieved through dynamical relaxation in an initially circular disk with a moderately top-heavy mass function.Comment: 65 pages, 22 figures, 8 tables, submitted to Ap