At a time when so much of the prestigious astronomical research is devoted to new and highly speculative phenomena, it has been rewarding to see and hear the cautions and accurate approach to the measuring and interpreting of stellar quantities. It has been shown by many speakers, perhaps clearest of all by our participant of honor Professor Popper, how insufficient attention to calibration problems can lead to erroneous results.

Calibration of Fundamental Stellar Quantities: Summary and Conclusions

Space-based astronomical instruments and gravitational experiments require dramatically improved distance measurement accuracy. The Tracking Frequency laser distance Gauge measures to picometer accuracy. We discuss the design of the semiconductor laser version and its controller.

Semiconductor laser tracking frequency distance gauge

: This paper describes a package for analytical ray tracing of relatively simple optical systems AESOP (An Extensible Symbolic Optics Package) enables analysis of the effects of small optical element misalignments or other perturbations (It is possible to include two or more simultaneous independent perturbations) Wavefront aberrations and optical path variations can be studied as functions of the perturbation parameters The power of this approach lies in the fact that the results can be manipulated algebraically, allowing determination of misalignment tolerances as well as developing physical intuition, especially in the picometer regime of optical path length variations

https://www.usno.navy.mil/USNO/astronomical-applications/publications/reports/MMAESOP_article.pdf

Analytical Study of Optical Wavefront Aberrations Using Maple

For nearly a century astronomers have expended considerable effort to determine the size of the Milky Way. This effort is worthwhile because any change in the value of the distance from the Sun to the center of the Galaxy, Ro, has widespread impact on astronomy and astrophysics. All distances determined from observed radial velocities and a rotation model of the Galaxy are directly proportional to Ro. Most estimates of the gravitational and luminous mass of the Galaxy scale with Ro. Similarly, the mass and luminosity of objects within the Galaxy, such as giant molecular clouds and the nonthermal source at the Galactic center depend on Ro• On a larger scale, since extragalactic distances are based on Galactic calibrations, the Hubble constant and Ro are interrelated. Indeed, it may be possible to use the size of the Milky Way as an extragalactic "meter stick" and determine distances to similar spiral galaxies (e.g. de Vaucouleurs 1 983a,b; van der Kruit 1 986). Historically, astronomers have measured distances to nearby stars, used these distances to calibrate their luminosities, and estimated Ro from the spatial distributions of stars and globular clusters. Recently, however, direct measurements of Ro have become feasible and the possibility of using Ro as a distance standard has emerged. For example, if one knew Ro very accurately, one could recalibrate the absolute magnitudes of Cepheid,

The Distance to the Center of the Galaxy

Advanced astronomical missions with greatly enhanced resolution and physics missions of unprecedented accuracy will require laser distance gauges of substantially improved performance. We describe a laser gauge, based on Pound–Drever–Hall locking, in which the optical frequency is adjusted to maintain an interferometer’s null condition. This technique has been demonstrated with pm performance. Automatic fringe hopping allows it to track arbitrary distance changes. The instrument is intrinsically free of the nm-scale cyclic bias present in traditional (heterodyne) high-precision laser gauges. The output is a radio frequency, readily measured to sufficient accuracy. The laser gauge has operated in a resonant cavity, which improves precision, can suppress the effects of misalignments, and makes possible precise automatic alignment. The measurement of absolute distance requires little or no additional hardware, and has also been demonstrated. The proof-of-concept version, based on a stabilized HeNe laser and ...

Tracking frequency laser distance gauge

POINTS (Precision Optical INTerferometer in Space) would perform microarcsecond optical astrometric measurements from space, yielding submicroarcsecond astrometric results from the mission. It comprises a pair of independent Michelson stellar interferometers and a laser metrology system that measures both the critical starlight paths and the angle between the baselines. The instrument has two baselines of 2 m, each with two subapertures of 35 cm; by articulating the angle between the baselines, it observes targets separated by 87 to 93 deg. POINTS does global astrometry, i.e., it measures widely separated targets, which yields closure calibration, numerous bright reference stars, and absolute parallax. Simplicity, stability, and the mitigation of systematic error are the central design themes. The instrument has only three moving-part mechanisms, and only one of these must move with sub-milliradian precision; and other two can tolerate a precision of several tenths of a degree. Optical surfaces preceding the beamsplitter or its fold flat are interferometrically critical; on each side of the interferometer, there are only three such. Thus, light loss and wavefront distortion are minimized. POINTS represents a minimalistic design developed ab initio for space. Since it is intended for astrometry, and therefore does not require the u-v-plane coverage of an imaging instrument, each interferometer need have only two subapertures. The design relies on articulation of the angle between the interferometers and body pointing to select targets; the observations are restricted to the `instrument plane.' That plane, which is fixed in the pointed instrument, is defined by the sensitive direction for the two interferometers. Thus, there is no need for siderostats and moving delay lines, which would have added many precision mechanisms with rolling and sliding parts that would be required to function throughout the mission. Further, there is no need for a third interferometer, as is required when out-of-plane observations are made. An instrument for astrometry, unlike those for imaging, can be compact and yet scientifically productive. The POINTS instrument is compact and therefore requires no deployment of precision structures, has no low-frequency (i.e., under 100 Hz) vibration modes, and is relatively easy to control thermally. Because of its small size and mass, it is easily and quickly repointed between observations. Further, because of the low mass, it can be economically launched into high Earth orbit which, in conjunction with a solar shield, yields nearly unrestricted sky coverage and a stable thermal environment.

POINTS: high astrometric capacity at modest cost via focused design

Newcomb is a design concept for a low-cost astrometric optical interferometer with nominal single-measurement accuracy of 100 microseconds of arc ((mu) as). In a 30 month mission, it will make scientifically interesting measurements of O-star, RR Lyrae, and Cepheid distances, probe the dark matter in our Galaxy via parallax measurements of K giants in the disk, establish a reference grid with internal consistency better than 50 microsecond(s) , and lay groundwork for the larger optical interferometers that are expected to produce a profusion of scientific results during the next century. With an extended mission life, Newcomb could do a useful preliminary search for other planetary systems.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Newcomb: a small astrometric interferometer

POINTS: a small low-cost spaceborne astrometric optical interferometer

Popular Tasks used by Researchers

How can I help with your research?

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

We encountered an error while loading the panel. Please try refreshing the page.

Something went wrong

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

Anyone with the link can view this chat. You can switch it back to private anytime.

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

Robert J. Zielinski

Author Tools

Chat about Author

Papers

POINTS: high astrometric capacity at modest cost via focused design

Newcomb: a small astrometric interferometer

POINTS: a small low-cost spaceborne astrometric optical interferometer