# Typography: general typing rules

Fine tuning of the text

The following should be used to improve the readability of the text:

 \, a thin space, e.g. between thousands in numbers with more than 4 digits; a line division will not be made following this space, -- en-dash; two hyphens, without a space at either end, -- Please note: in TEX, -- gives an em-dash "--"; we do not use this, but rather the shorter en-dash with spaces, i.e. space, two hyphens, for an en-dash, space, to give an "em-dash". - hyphen; no space at either end, $-$ minus, in the text only, ~ fixed space, e.g. between parts of names.

Their use is best explained in the following example.

Sample input:
20\,000 km, 1\,000\,000 s, HD 174\,638 1950--1985, p.~11--21 this -- written on a computer -- is now printed signal-to-noise ratio, early-type, metal-poor, non-relativistic $-30$~K, $-5\ ^{\circ}$C Dr.~h.c.~Rockefeller-Smith and Prof.~Dr.~Mallory

Sample output:
20000 km, 1000000 s, NGC 468324 1950-1985, p. 11-21 this - written on a computer - is now printed signal-to-noise ratio, early-type, metal-poor, non-relativistic -30 K, -5 °C Dr. h.c. Rockefeller-Smith and Prof. Dr. Mallory

Units, symbols, and nomenclature

Authors can considerably help the publisher by observing the following rules:
1. The text should make clear distinctions between physical variables, mathematical symbols, units of measurement, abbreviations, chemical formulae,

2. Italics and boldface should be used appropriately to identify physical or mathematical variables. In general, variables are set in regular italics, vectors in boldface italics. Physical constants such as the speed of light, the Boltzmann constant, the Hubble constant and the solar mass are also set in regular italics.

3. Italics should never be used for units of measurement e.g. km, erg cm-2, s-1 or for chemical formulae unless, of course, these items fall within a passage that is entirely in italics.

4. As far as possible, italics should be avoided for the following: mathematical signs such as "d" (total differential), "e" (base of natural logarithm), "i" (imaginary unit), "pi" (3.14159...), and abbreviations used as subscripts or superscripts to variables, but serving merely as labels, e.g. (d = dust), (e = electron). However, in conformity with the rest of the text, italics should be used if the subscripts or superscripts are variables themselves.

5. For common units of measurement (SI and non-SI), standard abbreviations should be used. Unusual units may, at the authors' discretion, be written in full, at least at the first mention. Some traditional, non-SI units persist in astronomy literature. Some are acceptable (e.g. erg, angström/Å) but others are obsolescent and should be avoided (e.g. micron/). Compound units in which the meaning "per" is implied can be written using either a slash or a negative index: A&A prefers the latter style, e.g. km s-1 instead of km/s.

6. For the correct naming of astronomical objects outside the solar system, it is suggested that authors refer to the recommendations on nomenclature given by the International Astronomical Union at http://cdsweb.u-strasbg.fr/Dic/how.htx .

Special typefaces
Emphasize:
(\emph{Emphasize}) should be used for emphasis in the text.

Vectors:
\vec{Symbol}, vectors may only appear in math mode.

Input examples:
$\vec{A} \times \vec{B} \cdot \vec{C}$
$\vec{A\/}^{\rm T} \otimes \vec{B} \otimes \vec{\hat D}$
Tensors:
\tens{Symbol}], tensors may only appear in math mode.

Input example:
\tens{ABC}
Ions:
\ion{<element symbol>}{<degree of ionization>}, the degree of ionization in the \ion command has to be given as lower case roman numerals (e.g. \ion{H}{ii} which yields H II).

Input examples:
\ion{H}{II}
\element[ ][13]{C}
Elements:
\element[<electrical charge>][<number of nucleons>] [<number of protons>]
[<number of neutrons>]{<element symbol>}

Note, that if you want to have for example 13C, the last two optional arguments may be omitted: \element[ ][13]{C}.

Signs and characters

You may need to use special signs. The available ones are listed in different books (LaTeX User's Guide & Reference Manual, The LaTeX Companion, etc.). We have created further common astronomy symbols:

 In Explanation Out In Explanation Out \sun sun symbol \fs fraction of second \degr degree \fdg fraction of degree \diameter diameter Ø \fp fraction of period \farcs fraction of arcsecond \fd fraction of day \farcm fraction of arcmin \arcsec arcsecond \fh fraction of hour \arcmin arcminute \fm fraction of minute

 In Out In Out \la \ga \cor \sol \sog \lse \gse \grole \leogr \loa \goa \getsto \lid \gid

## Mathematical formulae

All equations that you are referring to with \ref must have the corresponding \label - please use this mechanism only. Punctuate a displayed equation in the same way as ordinary text.
 \left(     \left[ \right)     \right]

Note that the sizes of the parentheses or other delimiter symbols used in equations should ideally match the height of the formulas being enclosed. This is automatically taken care of by these LaTeX commands.

Italic and roman type in the math mode

In math mode LaTeX treats all letters as though they were mathematical or physical variables; hence they are typeset in italics. However, any textual elements within formulas should be set in roman. Roman should also be used for subscripts and superscripts in formulas where these are merely labels and not in themselves variables, e.g.
 $T_\mathrm{eff} = 5\times 10^{9}\ \mathrm{K}$ produces $T_\mathrm{K}$ produces TK (K = Kelvin) $m_\mathrm{e}$ produces me (e = electron)
However, do not use roman if the subscripts or superscripts represent variables, e.g. . Please ensure that physical units (e.g. pc, erg s-1 K, cm-3, W m-2 Hz-1, m kg s-2 A-2) and abbreviations such as Ord, Var, GL, SL, sgn, const. are always set in roman type with an appropriate inter-word spacing. To ensure this, use the \mbox command: \mbox{Hz}.
On p. 44 of the LaTeX User's Guide & Reference Manual (2nd ed.) by Leslie Lamport, you will find the names of common mathematical functions, such as log, sin, exp, max, and sup. These should be coded as \log, \sin, \exp, \max, \sup and will then automatically appear in roman.
In order to distinguish "d" used as the "differential sign" and "e" used as the "exponential function" from normal variables, set these letters in roman. Chemical symbols and formulas should be set in roman, e.g. Fe not Fe, H2O not H2O, H not H.