Observational details for the spectroscopically-confirmed galaxies are given in Table 3 , including estimates of their redshifts z using the diagnostic emission or absorption features as indicated.
We could potentially use the estimated absolute magnitude of LP 26 to coarsely constrain its spectral type, but we are unfortunately limited to Galactic results e. Walborn ; Wegner ; Martins et al.
Also shown in Fig. The models at the ZAMS have near constant luminosities, but such stars will have different bolometric corrections BCs due to the increasing temperatures towards lower metallicity. Alternatively, this also implies that fewer massive stars could potentially account for a given level of ionisation in unresolved systems at very low- Z. We are currently unable to link initial mass to spectral type as a function of metallicity, but the differences above echo the effect where metallicity is known to impact on the temperature scale of OB-type stars of a given spectral type e.
Massey et al. Taking this into consideration for the calibrations from Martins et al. Given the prevalence of binarity in massive stars, McQuinn et al. Such a mass exceeds the maximum of 2. Aside from the specific physical properties of LP 26, its spectroscopic confirmation as an O-type star supports the conclusions of McQuinn et al. The known H II region is the compact blue source in the main southern feature.
Intensity and velocity maps for the ionised gas in Leo P. Left-hand panels : intensity of the given emission line; right-hand panels : differential velocities from Gaussian fits to the observed lines.
Adopting a distance of 1. The northern and southern shells appear to be fairly well defined rings of emission, whereas a central shell appears somewhat more diffuse. The H II region is located on northern edge of the southern ring.
The positions of our spectroscopically-confirmed stars are overlaid in the left-hand panels of Fig. The absence of massive stars in the northern shell suggests this is an older formation e. Indeed, given the large number of high-mass x-ray binaries with Be-type components in the low-metallicity environment of the SMC e. Coe et al. Lastly, we also note the four stars along the southern edge of the southern ring, suggestive of a connection in their formation.
Using a similar profile-fitting approach to that used by Castro et al. Prompted by the discovery of these spatially-distinct structures we re-examined the HST photometry of all the stars in the four regions i. This led to relatively sparse samples and aside from reinforcing the relative dearth of luminous, blue stars in the northern and southern regions, we were unable to glean further insights into the histories of these regions.
We have presented the first stellar spectroscopy in Leo P, a low luminosity, dwarf galaxy at a distance of 1. From consideration of its absolute magnitude and assuming the published distance , this is probably a mid O-type star Fig. Confirmation of two candidate AGB stars from Lee as carbon stars, and confirmation of two further candidates as luminous cool presumably AGB stars via detection of CaT absorption in their spectra Figs.
In particular, we highlight future observations of the O-type star LP 26 to derive its physical properties and a more robust estimate of its mass cf. Moreover, to interpret such observations we will also require synthetic spectra at this low metallicity from the latest model-atmosphere codes. Quantitative analysis to determine their physical parameters in part to calibrate low- Z evolutionary models and detailed kinematic analysis to investigate the dynamical properties of the cool population will again require ambitious spectroscopic follow-up.
Ultimately we also want ultraviolet spectroscopy of the population of massive stars in Leo P, to investigate their wind properties as well as their physical parameters in this important low-metallicity regime. DRW is supported by a fellowship from the Alfred P. Sloan Foundation, and acknowledges support from the Alexander von Humboldt Foundation.
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Introduction 2. General structure 4. UK versus US spelling and grammar 5. Punctuation and style concerns regarding equations, figures, tables, and footnotes 6.
Verb tenses 7. General hyphenation guide 8. Common editing issues 9. Measurements and their descriptions Top Abstract 1. Observations and Spectral content 4. Expected absolute Nebular emission 6. Nature makes beautiful ones we call rainbows. Sunlight sent through raindrops is spread out to display its various colors the different colors are just the way our eyes perceive radiation with slightly different energies.
Spectroscopy can be very useful in helping scientists understand how an object like a black hole, neutron star, or active galaxy produces light, how fast it is moving, and what elements it is composed of. Spectra can be produced for any energy of light, from low-energy radio waves to very high-energy gamma rays.
Each spectrum holds a wide variety of information. For instance, there are many different mechanisms by which an object, like a star, can produce light. Each of these mechanisms has a characteristic spectrum. White light what we call visible or optical light can be split up into its constituent colors easily and with a familiar result: the rainbow.
All we have to do is use a slit to focus a narrow beam of the light at a prism. This setup is actually a basic spectrometer. The resultant rainbow is really a continuous spectrum that shows us the different energies of light from red to blue present in visible light. But the electromagnetic spectrum encompasses more than just optical light.
It covers all energies of light, extending from low-energy radio waves, to microwaves, to infrared, to optical light, to ultraviolet, to very high-energy X-rays and gamma rays.
Three types of spectra: continuous, emission line and absorption. Each element in the periodic table can appear in gaseous form and will produce a series of bright lines unique to that element.
This has the effect of blurring the sharpness of each emission line into a broad band of wavelengths. The same thing happens to neighbouring lines so that by the time the light emerges from the gas it has 'smeared out' into a continuous spectrum at all wavelengths. Emission Spectra In a gas containing only atoms of one kind, the electrons will all be in their ground state if the temperature is low.
As the gas is heated, its atoms gain kinetic energy and collide with their neighbours causing their electrons to be raised to excited states. As the electrons drop down, photons will be emitted with many different energies and wavelengths corresponding to the particular electron energy level scheme for the gas. The emission of these lines will cause the gas to glow with a light composed of wavelengths that correspond to the electron energy transitions. For moderate temperatures we might find that only the first excited state of the atom is attained and so the emission light will consist of a single bright emission line corresponding to the difference in energies between the first excited and ground states.
As the temperature is increased, more emission lines will start to appear until at higher temperatures many lines will be visible corresponding to all the allowed energy transitions of electrons in the gas.
In this way an emission line spectrum is formed that is related to the elemental composition of the gas. Absorption Spectra To explain Kirchoff's third rule we need to consider what happens when we place a gas of unknown composition in front of a source of light that emits a continuous spectrum.
Light from the continuous source contains photons of all energies and wavelengths. Now if it is the case that the energy of some of these photons is exactly equal to the difference between the ground state and an excited state of an atom in the unknown gas, then that photon will be removed from the incident light. The excited electron will quickly return to the ground state emitting a photon however, the emitted photon need not be emitting along the same direction as the absorbed photon but is usually emitted in a different direction.
The re-emitted photons are not therefore, generally observed through a spectroscope at the source, and the continuous spectrum is observed when looking to have dark lines at the wavelengths corresponding to excited states of the atoms in the unknown gas. It follows that it is precisely these wavelengths at which light would be emitted in an emission spectrum if the unknown gas was heated to a high temperature.
Both the dark lines superimposed on the continuous spectrum and the bright lines in the emission spectrum provide a 'spectral fingerprint' that identifies the elements present in a hot gas.
The first star to be studied spectroscopically was the sun. A British astronomer William Hyde Woollaston , using a prism, observed that the sun emitted a continuous spectrum that had dark lines which are now known as Fraunhofer lines.
Fraunhofer realised that some of these dark lines were at the same position in wavelength as bright emission lines of spectra of various elements which were studied in the laboratory. Astrophysicists have now observed thousands of dark absorption lines in the sun's spectrum. Using Kirchoff's rules they have been able to detect the presence of 67 elements in the sun. As an interesting footnote, the element helium was first discovered in the sun before it was found on earth.
An unknown line in the sun's spectrum was observed which could not be related to lines of elements then known in the laboratory. It was named helium after the Greek word for the sun helios , and was subsequently discovered on earth forty years later!
When we observe the spectra of other stars we find that some are like the sun and others are very different. Vega for example, is a very hot star in the constellation Lyre and a pair of binoculars will easily show it glowing with a bluish tinge. The sun's spectrum shows two lines of hydrogen The spectrum of Vega, however, has the same two lines but they are much thicker and more intense. At first sight one might think that the thicker hydrogen lines mean that there is a greater abundance of hydrogen in Vega than in the sun.
Actually, this is not the case and the composition of most stars are broadly similar in their chemical mixtures.
It turns out in fact, that the thickness of the lines are related to the star's temperature. The For cool stars whose surface temperatures are low to moderate, most of the hydrogen atoms will be in the ground state.
As a result the Lyman series which consist only of lines involving transitions from the ground state will figure prominently in the spectrum. As a result, these stars will show the Molecular Spectra Some stars display banded spectral features of many finely spaced lines.
These are caused by molecules in the outer layers of a star. While a molecule consists of atoms with excited electronic states, it also has collective rotational and vibrational motion which is also quantised.
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